0001193125-26-057329 | 10-K | XBRL Viewer | Ultragenyx Pharmaceutical INC

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Investment in Amlogenyx. Inc. - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Jul. 31, 2024
Schedule of Investments [Line Items]
Total assets	$ 1,532.0	$ 1,503.0
Total liabilities	1,605.0	1,241.0
Amlogenyx Inc [Member]
Schedule of Investments [Line Items]
Shares received			9.0
Contributed by affiliated entities			$ 7.0
Total assets	$ 5.0	$ 14.0
Amlogenyx Inc [Member] \| Third-Party Investor [Member]
Schedule of Investments [Line Items]
Estimated fair value			$ 7.0
Amlogenyx Inc [Member] \| Series Seed Preferred Stock [Member]
Schedule of Investments [Line Items]
Shares received			1.6

- Definition

Amount of asset recognized for present right to economic benefit.

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Cost of the investment.

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Fair value of investment in security owned.

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+ Details

Net Loss per Share

12 Months Ended

Dec. 31, 2025

Earnings Per Share [Abstract]

Net Loss per Share

17.

Net Loss per Share

The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2025, 2024, and 2023 (in millions, except per share data):


	Year Ended December 31,
	2025			2024			2023
Numerator:
Net loss	$	(575	)	$	(569	)	$	(607	)
Denominator:
Weighted-average shares used to compute net loss per share, basic and diluted		98.6			90.5			73.5
Net loss per share, basic and diluted	$	(5.83	)	$	(6.29	)	$	(8.25	)

The following weighted-average outstanding common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive (in millions):


	Year Ended December 31,
	2025		2024		2023
Options to purchase common stock, restricted stock units, and performance stock units		16.8		16.3		14.2

Cybersecurity Risk Management, Strategy and Governance	12 Months Ended
Cybersecurity Risk Management, Strategy and Governance	Dec. 31, 2025
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	Item 1C. Cybersecurity In the ordinary course of our business, we collect, use, store, and transmit digitally large amounts of confidential, financial, sensitive, proprietary, personal, and health-related information. The secure maintenance of this information and our information technology systems is important to our operations and business strategy. To this end, we have implemented processes designed to assess, identify, and manage risks from potential unauthorized occurrences on or through our information technology systems that may result in adverse effects on the confidentiality, integrity, and availability of these systems and the data residing therein. Our cybersecurity program is informed by industry standards and best practices, such as the National Institute of Standards and Technology (NIST) Cybersecurity Framework. This program is managed and monitored by a dedicated information technology team, including an Executive Director of IT Infrastructure and Cybersecurity, and is led by our Senior Vice President, Chief Information Officer, or CIO. Our processes include mechanisms, controls, technologies, and systems designed to prevent or mitigate data loss, theft, misuse, or other security incidents or vulnerabilities affecting the data and maintain a stable information technology environment. Our program includes, for example: • Regular penetration and vulnerability testing, data recovery testing, security audits, and ongoing risk assessments; • Engagement of external service providers, where appropriate, to assess, test or otherwise assist with aspects of our security controls as part of our operational security model; • Cybersecurity awareness training for our employees, contactors, incident response personnel, and senior management; • A cybersecurity incident response plan that includes procedures for responding to cybersecurity incidents and annual tabletop exercises with participants from cross functional teams; • A third-party risk management process for service providers, suppliers, and vendors including due diligence prior to engagement and ongoing periodic review of our key technology vendors, and other contractors and suppliers. Our CIO, together with our Executive Director of IT Infrastructure and Cybersecurity and other members of the IT leadership team, are responsible for assessing and managing cybersecurity risks. Our CIO has over ten years of experience managing information technology and cybersecurity. Our Executive Director of IT Infrastructure and Cybersecurity has over 25 years of experience managing information technology and cybersecurity matters and is certified as a Certified Information Security Manager. We consider cybersecurity, along with other significant risks that we face, within our overall enterprise risk management framework. Since the beginning of the last fiscal year, we have not identified any risks from known cybersecurity threats, including as a result of any prior cybersecurity incidents, that have materially affected us, but we face certain ongoing cybersecurity risks or threats that, if realized, are reasonably likely to materially affect us. Additional information on cybersecurity risks we face is discussed in Part I, Item 1A, “Risk Factors,” under the heading “Our business and operations may be materially adversely affected in the event of computer system failures or security breaches.” The Board of Directors, as a whole and at the committee level, has oversight for the most significant risks facing us and for our processes to identify, prioritize, assess, manage, and mitigate those risks. The Audit Committee, which is comprised solely of independent directors, has been designated by our Board to oversee cybersecurity risks. The Audit Committee receives updates on cybersecurity and information technology matters and related risk exposures from our CIO on at least an annual basis. The Board also receives updates from the Audit Committee on cybersecurity risks on a regular basis.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	The Board of Directors, as a whole and at the committee level, has oversight for the most significant risks facing us and for our processes to identify, prioritize, assess, manage, and mitigate those risks. The Audit Committee, which is comprised solely of independent directors, has been designated by our Board to oversee cybersecurity risks. The Audit Committee receives updates on cybersecurity and information technology matters and related risk exposures from our CIO on at least an annual basis. The Board also receives updates from the Audit Committee on cybersecurity risks on a regular basis.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Board of Directors, as a whole and at the committee level, has oversight for the most significant risks facing us and for our processes to identify, prioritize, assess, manage, and mitigate those risks. The Audit Committee, which is comprised solely of independent directors, has been designated by our Board to oversee cybersecurity risks.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Audit Committee receives updates on cybersecurity and information technology matters and related risk exposures from our CIO on at least an annual basis. The Board also receives updates from the Audit Committee on cybersecurity risks on a regular basis.
Cybersecurity Risk Role of Management [Text Block]	Our CIO, together with our Executive Director of IT Infrastructure and Cybersecurity and other members of the IT leadership team, are responsible for assessing and managing cybersecurity risks. Our CIO has over ten years of experience managing information technology and cybersecurity. Our Executive Director of IT Infrastructure and Cybersecurity has over 25 years of experience managing information technology and cybersecurity matters and is certified as a Certified Information Security Manager. We consider cybersecurity, along with other significant risks that we face, within our overall enterprise risk management framework.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	This program is managed and monitored by a dedicated information technology team, including an Executive Director of IT Infrastructure and Cybersecurity, and is led by our Senior Vice President, Chief Information Officer, or CIO.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	Our CIO has over ten years of experience managing information technology and cybersecurity. Our Executive Director of IT Infrastructure and Cybersecurity has over 25 years of experience managing information technology and cybersecurity matters and is certified as a Certified Information Security Manager.

Revenue - Summary of Disaggregation of Total Revenues from Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation Of Revenue [Line Items]
Total revenues	$ 673	$ 560	$ 434
Collaboration and license
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	71
Collaboration and license \| Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	70
Collaboration and license \| Other
Disaggregation Of Revenue [Line Items]
Total revenues	0	0	1
Product Revenue
Disaggregation Of Revenue [Line Items]
Total revenues	369	285	180
Product Revenue \| Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	177	135	75
Product Revenue \| Mepsevii
Disaggregation Of Revenue [Line Items]
Total revenues	37	30	30
Product Revenue \| Dojolvi
Disaggregation Of Revenue [Line Items]
Total revenues	96	88	71
Product Revenue \| Evkeeza
Disaggregation Of Revenue [Line Items]
Total revenues	59	32	4
Royalty revenue
Disaggregation Of Revenue [Line Items]
Total revenues	304	275	183
Royalty revenue \| Crysvita
Disaggregation Of Revenue [Line Items]
Total revenues	$ 304	$ 275	$ 183

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2025	Feb. 13, 2026	Jun. 30, 2025
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2025
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Trading Symbol	RARE
Entity Registrant Name	Ultragenyx Pharmaceutical Inc.
Entity Central Index Key	0001515673
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		96,629,788
Entity Public Float			$ 3.4
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.001 par value
Entity File Number	001-36276
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-2546083
Entity Address, Address Line One	60 Leveroni Court
Entity Address, City or Town	Novato
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94949
City Area Code	415
Local Phone Number	483-8800
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement relating to its 2026 Annual Meeting of Stockholders, to be held on or about May 14, 2026, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	San Mateo, California
Auditor Opinion [Text Block]	Opinion on the Financial Statements We have audited the accompanying consolidated balance sheets of Ultragenyx Pharmaceutical Inc. (the Company) as of December 31, 2025 and 2024, the related consolidated statements of operations, comprehensive loss, stockholders' equity and cash flows for each of the three years in the period ended December 31, 2025, and the related notes (collectively referred to as the “consolidated financial statements”). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2025 and 2024, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2025, in conformity with U.S. generally accepted accounting principles. We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control—Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 framework), and our report dated February 18, 2026 expressed an unqualified opinion thereon.

Stock-Based Awards - Summary of Activity Under PSUs from 2014 Plan (Details) - Performance Stock Units shares in Millions	12 Months Ended
	Dec. 31, 2025 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance \| shares	0.6
Number of shares, granted \| shares	0.4
Number of shares, vested \| shares	(0.2)
Number of shares, cancelled \| shares	(0.1)
Outstanding, Number of Shares, Unvested, Ending Balance \| shares	0.7
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance \| $ / shares	$ 59.39
Weighted-Average Grant Date Fair Value, granted \| $ / shares	50.77
Weighted-Average Grant Date Fair Value, vested \| $ / shares	53.44
Weighted-Average Grant Date Fair Value, cancelled \| $ / shares	49.95
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Ending Balance \| $ / shares	$ 57.48

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2025

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Company's Equity Plans

The table below summarizes the Company's equity plans as of December 31, 2025:


Plan	Year of Adoption	Expiration Date, as Amended	Maximum Number of Shares Authorized (millions)		Shares Available for Future Issuance (millions)
Employment Inducement Plan	2021	February 3, 2031		1.7		0.3
2023 Incentive Plan(1)	2023	June 7, 2033		15.5		7.9
2014 Employee Stock Purchase Plan	2014	June 7, 2033		7.3		6.2
(1) Maximum number of shares authorized and shares available for future issuance under the 2023 Incentive Plan includes 4.0 million shares subject to the 2014 Incentive Plan cancelled after June 7, 2023.

Summary of Activity Under Stock Option Plans Including 2011 Plan, 2014 Plan and 2023 Plan

Stock Option Activity

The following table summarizes activity under the Company’s stock option plans and related information:


	Options Outstanding
	Number of Options (millions)			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (In millions)
Outstanding — December 31, 2024		9.4		$	65.54	6	$	2
Options granted		1.2			41.75
Options exercised		—			38.57
Options cancelled		(1.7	)		73.53
Outstanding — December 31, 2025		8.9			60.87	6		—
Vested and exercisable — December 31, 2025		6.5			66.31	5		—
Vested and expected to vest — December 31, 2025		8.7			61.24	6		—

Summary of Company's Options Exercised and Vested

The following table summarizes the Company's options exercised and vested for each of the periods indicated (in millions except for weighted-average estimated fair value of options granted):


	Year Ended December 31,
	2025		2024		2023
Intrinsic value of options exercised	$	—	$	1	$	5
Cash received from the exercise of options	$	—	$	6	$	3
Weighted-average estimated fair value of options granted	$	22.92	$	29.88	$	25.53
Estimated fair value of options vested	$	46	$	54	$	60

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Cost of sales	$	2	$	1	$	1
Research and development		84		87		75
Selling, general and administrative		67		70		59
Total stock-based compensation expense	$	153	$	158	$	135

Fair Value of Stock Option Awards Granted Estimated Using Black-Scholes Option-Pricing Model

The fair value of stock option awards granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:


	Year Ended December 31,
	2025	2024	2023
Expected term (years)	6	6	6
Expected volatility	53%	55%	55%
Risk-free interest rate	4.1%	4.2%	4.2%
Expected dividend rate	0.0%	0.0%	0.0%

Restricted Stock Units

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Activity Under Stock Units from 2014 Plan

The following table summarizes activity under the Company’s Restricted Stock Units, or RSU, plans and related information:


	RSUs Outstanding
	Number of Shares (millions)			Weighted-Average Grant Date Fair Value
Unvested — December 31, 2024		5.2		$	53.22
RSUs granted		2.9			41.04
RSUs vested		(1.5	)		56.39
RSUs cancelled		(0.7	)		49.78
Unvested — December 31, 2025		5.9			46.23

Performance Stock Units

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Activity Under Stock Units from 2014 Plan

The following table summarizes activity under the Company’s Performance Stock Units, or PSUs and related information:


	PSUs Outstanding
	Number of Shares (millions)			Weighted-Average Grant Date Fair Value
Unvested — December 31, 2024		0.6		$	59.39
PSUs granted		0.4			50.77
PSUs vested		(0.2	)		53.44
PSUs cancelled		(0.1	)		49.95
Unvested — December 31, 2025		0.7			57.48

Performance Stock Options [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Activity Under Stock Option Plans Including 2011 Plan, 2014 Plan and 2023 Plan

The following table summarizes activity under the Company’s Performance Stock Option, or PSO, plans and related information:


	PSOs Outstanding
	Number of Options (millions)			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding — December 31, 2024		1.2		$	67.37	2	$	—
PSOs cancelled		(0.4	)		67.37
Outstanding — December 31, 2025		0.8			67.37	1		—
Vested and exercisable — December 31, 2025		0.8			67.37	1		—
Vested and expected to vest — December 31, 2025		0.8			67.37	1		—

Intangible Assets, Net - Schedule of Expected Amortization of the Intangible Assets (Details) $ in Thousands	Dec. 31, 2025 USD ($)
Intangible Assets, Net (Excluding Goodwill) [Abstract]
2026	$ 8
2027	7
2028	7
2029	7
2030	7
Thereafter	11
Total	$ 47

Stock-Based Awards - Summary of Company's Equity Plans (Parenthetical) (Details) shares in Millions	12 Months Ended
	Dec. 31, 2025 shares
2023 Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of shares authorized and shares available for future issuance	4.0
Expiration date, as amended	Jun. 07, 2033
2014 Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration date, as amended	Jun. 07, 2023

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

License and Research Agreements - Kyowa Kirin Co., Ltd. - Additional Information (Details) - License Agreement - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Jul. 01, 2022	Nov. 30, 2025	Dec. 31, 2025	Dec. 31, 2023	Dec. 31, 2024
Royalty Revenue in European Territory
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty on net sales receives			10.00%
Kyowa Kirin Collaboration
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales			30.00%	30.00%
Kyowa Kirin Collaboration \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered double-digit revenue share percentage entitled to receive			20.00%
Kyowa Kirin Collaboration \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tiered double-digit revenue share percentage entitled to receive			30.00%
Kyowa Kirin Collaboration \| Other Current Assets
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement other receivables			$ 1		$ 2
Kyowa Kirin Collaboration \| Royalty
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement accounts receivable			98		85
Kyowa Kirin Collaboration \| Commercial and Development Activity Reimbursements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License agreement accrued liabilities			$ 12		$ 7
Kyowa Kirin Collaboration \| Profit Share Territory
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining profit or loss share percentage on commercializing products			50.00%
Percentage of right to receive royalty payments on net sales	30.00%	25.00%

Equity (Tables)

12 Months Ended

Dec. 31, 2025

Equity [Abstract]

Summary of Pre- Funded Warrants Activity

The table below summarizes pre-funded warrants activity:


	Pre-funded warrants (millions)
As of December 31, 2023		1.7
Issuance of pre-funded warrants		1.5
As of December 31, 2024		3.2
Changes and adjustments		—
As of December 31, 2025		3.2

Accumulated Other Comprehensive (Loss) Income - Schedule of Total Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Cumulative foreign currency translation adjustment	$ 1	$ (2)
Unrealized gain (loss) on securities available-for-sale	(0)	1
Total accumulated other comprehensive (loss) income	$ 1	$ (1)

- Definition

Amount, after tax, of accumulated increase (decrease) in equity from transaction and other event and circumstance from nonowner source.

+ References + Details

License and Research Agreements - Abeona - Additional Information (Details) - Abeona - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2022	Dec. 31, 2025
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible future milestone payments		$ 1.0
License and Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of royalty on net sales receives		10.00%
Commercial milestone payments	$ 30.0

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Consolidation

The Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiaries. The Company consolidates any variable interest entity, or VIE, for which it is the primary beneficiary. Certain reclassifications have been made to prior periods in the consolidated financial statements and accompanying notes to conform with the current presentation.

Segment Reporting

The Company operates as one reportable segment relating to the research, development and commercialization of its products. The segment derives its current revenues from its four commercially approved products.

The Company’s Chief Operating Decision Maker, or CODM, is the Company's Chief Executive Officer. The CODM manages the Company’s operations on an integrated basis for the purpose of allocating resources. When evaluating the Company’s financial performance, the CODM regularly reviews total revenues and total expenses and makes decisions using this information on a consolidated basis.

Use of Estimates

The accompanying Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP. The preparation of the Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the Consolidated Financial Statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, stock-based compensation, revenue recognition, and the liabilities for sales of future royalties. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts.

Restricted cash primarily consists of money market accounts used as collateral for the Company’s obligations under its facility leases and to guarantee the fulfillment of certain sales orders to certain government-sponsored customers.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows (in millions):


	December 31,
	2025		2024		2023
Cash and cash equivalents	$	421	$	174	$	214
Restricted cash included in other current assets		13		7		2
Restricted cash included in other non-current assets		2		3		3
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	436	$	184	$	219

Marketable Securities

All marketable securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments at the time of purchase and reevaluates such designation as of each balance sheet date. Investments with a maturity of one year or less from the balance sheet date are reported as current marketable securities and investments with a maturity of greater than one year from the balance sheet date are reported as non-current marketable securities. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other expense. The cost of securities sold is based on the specific-identification method. Interest on investments is included in interest income.

Equity Investments

The Company records investments in equity securities, other than equity method investments, at fair market value, using market quotes when readily determinable. Equity securities with no readily determinable fair values are recorded using the measurement alternative of cost adjusted for observable price changes in orderly transactions for identical or similar investments of the same issuer less impairment, if any. Investments in equity securities are recorded in other assets on the Company's Consolidated Balance Sheets. Unrealized gains and losses are reported in change in fair value of equity investments on the Company’s Consolidated Statements of Operations. The Company regularly reviews its non-marketable equity securities for indicators of impairment.

Concentration of Credit Risk, Credit Losses, and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, and investments. The Company’s cash, cash equivalents, and investments are held by financial institutions that management believes are of high credit quality. The Company’s investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as U.S. government obligations, money market instruments and funds, corporate bonds, commercial paper, and asset-backed securities and places restrictions on maturities and concentrations by type and issuer. Such deposits may, at times, exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents, corporate issuers, and other financial instruments, to the extent recorded in the Consolidated Balance Sheets.

The Company is exposed to credit losses primarily through receivables from customers and collaborators and through its available-for-sale debt securities. For trade receivables and other financial instruments, the Company uses a forward-looking expected loss model that recognizes a current period charge for losses that are expected to be incurred over the life of the financial instrument.

The Company’s expected loss allowance methodology for the receivables is developed using historical collection experience, current and future economic market conditions, a review of the current aging status and financial condition of the entities. Specific allowance amounts are established to record the appropriate allowance for customers that have a higher probability of default. Balances are written off when determined to be uncollectible. The Company’s expected loss allowance methodology for the debt securities is developed by reviewing the extent of the unrealized loss, the size, term, geographical location, and industry of the issuer, the issuers’ credit ratings and any changes in those ratings, as well as reviewing current and future economic market conditions and the issuers’ current status and financial condition. There were no material credit losses recorded for receivables and available-for-sale debt securities which were attributable to credit risk for the years ended December 31, 2025 and 2024.

For available-for-sale debt securities with unrealized losses, the losses are recognized as allowances rather than as reductions in the amortized cost of the securities. There was no allowance for losses on available-for-sale debt securities which were attributable to credit risk for the years ended December 31, 2025 and 2024.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Inventory

The Company values inventory at the lower of cost and net realizable value and determines the cost of inventory using the average cost method. The Company expenses costs associated with the manufacture of product candidates prior to regulatory approval. Inventories consist of currently approved products. The Company periodically reviews its inventories for excess amounts or obsolescence and writes down obsolete or otherwise unmarketable inventory to its estimated net realizable value. Management determines excess inventory based on expected future demand. Estimates related to future demand are sensitive to significant inputs and assumptions such as acceptance by patients and physicians and the availability of formulary coverage and adequate reimbursement from private third-party payers for the product.

Property, Plant, and Equipment

Property, plant, and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the respective assets. Depreciation and amortization begins when the asset is placed in service. Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready to be placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the balance sheet and the resulting gain or loss, if any, is reflected in operations. See “Note 4. Balance Sheet Components” for further disclosure on the useful lives of property, plant, and equipment.

Intangible Assets

Finite-lived intangibles consist of contractual payments made in conjunction with license agreements and collaboration agreements. The contractual payments are recorded as intangible assets and are amortized over their estimated useful lives. The Company reviews its definite-lived intangible assets when events or circumstances may indicate that the carrying value of these assets is not recoverable and exceeds their fair value. The Company measures fair value based on the estimated future undiscounted cash flows associated with these assets in addition to other assumptions and projections that the Company deems to be reasonable and supportable.

Indefinite-lived intangibles consist of acquired in-process research and development, or IPR&D. IPR&D assets represent capitalized incomplete research projects that the Company acquired through business combinations. Such assets are initially measured at their acquisition date fair values and are tested for impairment annually and whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. When development of the project is complete, which generally occurs when regulatory approval to market a product is obtained, the associated assets will be deemed finite-lived and will be amortized over a period that best reflects the economic benefits provided by these assets.

If it is determined that an intangible asset becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of intangible assets to date.

Goodwill

Goodwill represents the excess of purchase price over fair value of net assets acquired in a business combination and is not amortized. Goodwill is subject to impairment testing at least annually during the fourth quarter or when a triggering event occurs that could indicate a potential impairment. If it is determined that the goodwill becomes impaired, the carrying value is written down to its fair value with the related impairment charge recognized in Consolidated Statements of Operations in the period in which the impairment occurs. The Company has not recorded any impairments of goodwill.

Impairment of Long-Lived Assets

The Company evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. The Company has not recorded material impairment of any long-lived assets.

Accruals of Research and Development Costs

The Company records accruals for estimated costs of research, preclinical and clinical studies and manufacturing development. These costs are a significant component of the Company’s research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations. The Company accrues the costs incurred under its agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. The Company determines the actual costs through obtaining information from external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services.

Liabilities for Sales of Future Royalties

The Company sold the right to receive certain royalty payments from net sales of Crysvita in certain territories to RPI Finance Trust, or RPI, an affiliate of Royalty Pharma, and to OCM LS23 Holdings LP, an investment vehicle for Ontario Municipal Employees Retirement System, or OMERS, as further described in “Note 10. Liabilities for Sales of Future Royalties.” At inception, the Company recorded a liability based upon estimated future cash flows discounted at a market rate. The liability is amortized using the effective interest method over the estimated life of the applicable arrangement. To determine the amortization of the liability, the Company estimates the total amount of future royalty payments to be received by the Company and paid to RPI and OMERS. Any estimated royalty payments in excess of the initial liability are recorded as non-cash interest expense. Consequently, the Company estimates imputed interest on the unamortized portion of the liabilities and records interest expense based on the estimated term of the arrangements.

The Company periodically assesses the expected royalty payments using a combination of historical results, internal projections and forecasts from external sources. To the extent such payments are greater or less than the Company’s initial estimates or the timing of such payments is materially different than its original estimates, the Company employs the prospective method to adjust the amortization of the liabilities and the effective interest rate.

Revenue Recognition

Product Sales

The Company sells its approved products through a limited number of distributors. Under Accounting Standards Codification, or ASC, 606, Revenue from Contracts with Customers, revenue from product sales is recognized at the point in time when control is transferred to these distributors. The Company also recognizes revenue from sales of certain products on a “named patient” basis, which are allowed in certain countries prior to the commercial approval of the product. Prior to recognizing revenue, the Company makes estimates of the transaction price, including any variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Product sales are recorded net of estimated government-mandated rebates and chargebacks, estimated product returns, and other deductions.

Provisions for returns and other adjustments are provided for in the period the related revenue is recorded, as estimated by management. These reserves are based on estimates of the amounts earned or to be claimed on the related sales and are reviewed periodically and adjusted as necessary. The Company’s estimates of government mandated rebates, chargebacks, estimated product returns, and other deductions depend on the identification of key customer contract terms and conditions, as well as estimates of sales volumes to different classes of payors. If actual results vary, the Company may need to adjust these estimates, which could have a material effect on earnings in the period of the adjustment.

Collaboration, License, and Royalty Revenue

The Company has certain license and collaboration agreements that are within the scope of ASC 808, Collaborative Agreements, which provides guidance on the presentation and disclosure of collaborative arrangements. Generally, the classification of the transactions under the collaborative arrangements is determined based on the nature of contractual terms of the arrangement, along with the nature of the operations of the participants. The Company records its share of collaboration revenue, net of transfer pricing related to net sales in the period in which such sales occur, if the Company is considered as an agent in the arrangement. The Company is considered an agent when the collaboration partner controls the product before transfer to the customers and has the ability to direct the use of and obtain substantially all of the remaining benefits from the product. Funding received related to research and development services and commercialization costs is generally classified as a reduction of research and development expenses and selling, general and administrative expenses, respectively, in the Consolidated Statements of Operations, because the provision of such services for collaborative partners are not considered to be part of the Company’s ongoing major or central operations.

The Company utilizes certain information from its collaboration partners to record collaboration revenue, including revenue from the sale of the product, associated reserves on revenue, and costs incurred for development and sales activities. For the periods covered in the financial statements presented, there have been no material changes to prior period estimates of revenues and expenses. The Company also records royalty revenues under certain of the Company’s license or collaboration agreements in exchange for the license of intellectual property.

As described in “Note 10. Liabilities for Sales of Future Royalties”, for certain royalty payments from net sales of Crysvita in applicable territories that were sold to RPI and OMERS, the Company records the non-cash royalty revenue on a prospective basis as royalty revenue in the Consolidated Statements of Operations over the term of the applicable arrangement.

The terms of the Company’s collaboration and license agreements may contain multiple performance obligations, which may include licenses and research and development activities. The Company evaluates these agreements under ASC 606, Revenue from Contracts with Customers, to determine the distinct performance obligations. The Company analogizes to ASC 606 for the accounting for distinct performance obligations for which there is a customer relationship. Prior to recognizing revenue, the Company makes estimates of the transaction price, including variable consideration that is subject to a constraint. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Total consideration may include nonrefundable upfront license fees, payments for research and

development activities, reimbursement of certain third-party costs, payments based upon the achievement of specified milestones, and royalty payments based on product sales derived from the collaboration.

If there are multiple distinct performance obligations, the Company allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The standalone selling price is generally determined based on the prices charged to customers or using expected cost-plus margin. The Company estimates the efforts needed to complete the performance obligations and recognizes revenue by measuring the progress towards complete satisfaction of the performance obligations using input measures.

Deferred Compensation Plan

The Company maintains a nonqualified deferred compensation plan whereby certain employees and members of the board of directors are able to defer certain equity awards and other compensation. Amounts deferred are invested into shares of the Company's common stock and corporate-owned life insurance. The plan complies with the provisions of Section 409A of the Internal Revenue Code. All the investments held in the plan are recorded in other non-current assets in the Consolidated Balance Sheets. The short-term portion of the corresponding liability for the plan is included in accrued expenses. The long-term portion of the liability is included in other non-current liabilities in the Consolidated Balance Sheets. Changes in the value of the deferred compensation assets and liabilities are recorded in earnings as they occur. Certain equity awards deferred under the plan are required to be settled through the issuance of Company stock. These awards are recorded as treasury stock and deferred compensation obligation within stockholders’ equity (deficit).

Leases

Lease agreements are evaluated to determine whether an arrangement is or contains a lease in accordance with ASC 842, Leases. The Company determines if an arrangement includes a lease at inception. Right-of-use lease assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. The right-of-use lease asset includes any lease payments made and excludes lease incentives. Incremental borrowing rate is used in determining the present value of future payments. The Company applies a portfolio approach to the property leases to apply an incremental borrowing rate to leases with similar lease terms. The lease terms may include options to extend or terminate the lease. The Company recognizes the options to extend the lease as part of the right-of-use lease assets and lease liabilities only if it is reasonably certain that the option would be exercised. Lease expense for minimum lease payments is recognized on a straight-line basis over the non-cancelable lease term. The Company has elected to not separate lease and non-lease components. See “Note 9. Leases” for further disclosure.

Comprehensive Loss

Comprehensive loss is the change in stockholders’ equity (deficit) from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive loss is comprised of unrealized gains and losses on investments in available-for-sale securities and foreign currency translation adjustments.

Research and Development

Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred. The deferred amounts are expensed as the related goods are delivered or the services are performed.

Stock-Based Compensation

Stock-based awards issued to employees, including stock options, performance stock options, or PSOs, restricted stock units, or RSUs, and performance stock units, or PSUs are recorded at fair value as of the grant date and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). PSOs and PSUs vest only if certain specified criteria are achieved and the employees’ continued service requirements are met; therefore, the expense recognition occurs when the likelihood of the PSOs and PSUs being earned is deemed probable. Stock compensation expense on awards expected to vest is recognized net of estimated forfeitures.

Income Taxes

The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance.

In conjunction with the acquisition of Dimension Therapeutics, Inc., or Dimension, a deferred tax liability was recorded reflecting the tax impact of the difference between the book basis and tax basis of acquired IPR&D. Such deferred income tax liability is not used to offset deferred tax assets when analyzing the Company’s valuation allowance as the acquired IPR&D is considered to have an indefinite life until the Company completes or abandons development of the acquired IPR&D.

The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

Foreign Currency

Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where the local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date, with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Income and expense accounts are translated at average exchange rates for the period. Transactions which are not in the functional currency of the entity are remeasured into the functional currency and gains or losses resulting from the remeasurement recorded in other expense.

Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Shares of common stock into which pre-funded warrants may be exercised are considered outstanding for the purposes of computing basic net loss per share because the shares may be issued for little or no consideration, are fully vested and are exercisable after the original issuance date. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive. In periods when we have incurred a net loss, options and warrants to purchase common stock are considered common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect is antidilutive.

Recent Accounting Pronouncements

In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, requiring public entities to disclose additional information about specific expense categories in the notes to the financial statements on an interim and annual basis. ASU 2024-03 is effective for fiscal years beginning after December 15, 2026, and for interim periods beginning after December 15, 2027, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2024-03.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures requiring public entities to disclose disaggregated information about their effective tax rate reconciliation and additional information about income taxes paid. Disclosure requirements will be applied on a prospective basis. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024. The Company adopted ASU 2023-09 during the year ended December 31, 2025.

License and Research Agreements - Schedule of Cost Sharing Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cost Sharing Payments [Line Items]
Cost of sales	$ 109	$ 77	$ 45
Kyowa Kirin Collaboration [Member]
Cost Sharing Payments [Line Items]
Research and development	(5)	(4)	(7)
Selling, general and administrative	0	(4)	(17)
Cost of sales	61	46	18
Regeneron Pharmaceuticals Inc
Cost Sharing Payments [Line Items]
Research and development	1	(3)	8
Cost of sales	$ 16	$ 8	$ 1

Intangible Assets, Net

12 Months Ended

Dec. 31, 2025

Intangible Assets, Net (Excluding Goodwill) [Abstract]

Intangible Assets, Net

Intangible Assets, net

Indefinite-lived Intangibles

As a result of the accounting for our acquisition of Dimension Therapeutics, Inc. in November 2017, the Company has IPR&D assets of $129 million as of December 31, 2025 and 2024. IPR&D assets represent the fair value of acquired programs to develop an AAV gene therapy for OTC deficiency and to develop an AAV gene therapy for glycogen storage disease type Ia. IPR&D assets are considered to be indefinite-life until the completion or abandonment of the associated research and development efforts.

Finite-lived Intangibles

Subsequent to the FDA approval of Dojolvi for the treatment of LC-FAOD in 2020, the Company recorded $5 million for the attainment of various development and commercial milestones as finite-lived intangible assets which are amortized over a weighted-average total useful life of 6 years.

In January 2022, the Company entered into a collaboration with Regeneron to commercialize Evkeeza for HoFH outside of the U.S. Pursuant to the collaboration agreement, the Company has incurred an upfront payment and regulatory and sales milestones to date totaling $63 million. As these payments are for the Company’s use of intellectual property for Evkeeza for HoFH, they were recorded as intangible assets, which are amortized over a weighted-average total useful life of 9 years.

The Company's intangible assets were as follows (in millions, except for years):


	December 31, 2025
	Gross Carrying Amount		Weighted-Average Life (Years)		Accumulated Amortization			Net Carrying Amount
Indefinite-lived intangibles	$	129		—	$	—		$	129
Finite-lived intangibles		68		9		(21	)		47
Total intangible assets	$	197		—	$	(21	)	$	176


	December 31, 2024
	Gross Carrying Amount		Weighted-Average Life (Years)		Accumulated Amortization			Net Carrying Amount
Indefinite-lived intangibles	$	129		—	$	—		$	129
Finite-lived intangibles		62		9		(13	)		49
Total intangible assets	$	191		—	$	(13	)	$	178

The Company recorded costs of sales of $8 million, $6 million and $4 million for the years ended December 31, 2025, 2024, and 2023, respectively, related to the amortization of intangible assets.

The expected amortization of intangible assets, as of December 31, 2025, for each of the next five years and thereafter is as follows (in millions):


2026	$	8
2027		7
2028		7
2029		7
2030		7
Thereafter		11
Total	$	47

Insider Trading Policies and Procedures	12 Months Ended
Insider Trading Policies and Procedures	Dec. 31, 2025
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Stock-Based Awards

12 Months Ended

Dec. 31, 2025

Share-Based Payment Arrangement [Abstract]

Stock-Based Awards

12.

Stock-Based Awards

Equity Plan Awards

Under the terms of the Company's 2023 Incentive Plan, or 2023 Plan, and Employment Inducement Plan, or Inducement Plan, awards may be granted at an exercise price not less than fair market value. The exercise price of an option may not be less than the fair market value. The term of an award granted under the 2023 Plan and Inducement Plan may not exceed ten years. Typically, the vesting schedule for option grants to employees provides that 1/4 of the grant vests upon the first anniversary of the date of grant, with the remainder of the shares vesting monthly thereafter at a rate of 1/48 of the total shares subject to the option. Typically, the vesting schedule for RSU grants provides that 1/4 of the grant vests upon the annual anniversary of the date of grant over the period of four years.

Under the 2014 Employee Stock Purchase Plan, or ESPP, eligible employees may purchase common stock at 85% of the lesser of the fair market value of common stock on the offering date or the purchase date with a six-month look-back feature. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. During the year ended December 31, 2025, the Company issued 0.2 million shares of common stock under the ESPP.

The table below summarizes the Company's equity plans as of December 31, 2025:


Plan	Year of Adoption	Expiration Date, as Amended	Maximum Number of Shares Authorized (millions)		Shares Available for Future Issuance (millions)
Employment Inducement Plan	2021	February 3, 2031		1.7		0.3
2023 Incentive Plan(1)	2023	June 7, 2033		15.5		7.9
2014 Employee Stock Purchase Plan	2014	June 7, 2033		7.3		6.2
(1) Maximum number of shares authorized and shares available for future issuance under the 2023 Incentive Plan includes 4.0 million shares subject to the 2014 Incentive Plan cancelled after June 7, 2023.

Stock Option Activity

The following table summarizes activity under the Company’s stock option plans and related information:


	Options Outstanding
	Number of Options (millions)			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (In millions)
Outstanding — December 31, 2024		9.4		$	65.54	6	$	2
Options granted		1.2			41.75
Options exercised		—			38.57
Options cancelled		(1.7	)		73.53
Outstanding — December 31, 2025		8.9			60.87	6		—
Vested and exercisable — December 31, 2025		6.5			66.31	5		—
Vested and expected to vest — December 31, 2025		8.7			61.24	6		—

The following table summarizes the Company's options exercised and vested for each of the periods indicated (in millions except for weighted-average estimated fair value of options granted):


	Year Ended December 31,
	2025		2024		2023
Intrinsic value of options exercised	$	—	$	1	$	5
Cash received from the exercise of options	$	—	$	6	$	3
Weighted-average estimated fair value of options granted	$	22.92	$	29.88	$	25.53
Estimated fair value of options vested	$	46	$	54	$	60

The aggregate intrinsic values of options outstanding, vested and exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock.

Performance Stock Options

The following table summarizes activity under the Company’s Performance Stock Option, or PSO, plans and related information:


	PSOs Outstanding
	Number of Options (millions)			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding — December 31, 2024		1.2		$	67.37	2	$	—
PSOs cancelled		(0.4	)		67.37
Outstanding — December 31, 2025		0.8			67.37	1		—
Vested and exercisable — December 31, 2025		0.8			67.37	1		—
Vested and expected to vest — December 31, 2025		0.8			67.37	1		—

During the year ended December 31, 2022, PSOs were granted to certain nonexecutive employees. PSOs are subject to vest only if specified operational milestones are achieved and the employees’ continued service with the Company. The Company uses the Black-Scholes method to calculate the fair value at the grant date and is recognizing stock-based compensation expense for the PSOs that are expected to vest. Stock-based compensation for PSOs is recognized over the service period, beginning in the period the Company determines it is probable that a milestone will be achieved. Forfeitures of PSOs are recognized as they occur. The Company reassesses the probability of the performance condition at each reporting period and adjusts the compensation cost based on the probability assessment. As of December 31, 2025, certain operational milestones had been achieved. The aggregate intrinsic values of PSOs outstanding, vested and exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the PSOs and the fair value of the Company’s common stock. The total estimated grant date fair value of PSOs vested during the years ended December 31, 2025, 2024, and 2023 was $14 million, $10 million, and $3 million, respectively.

Restricted Stock Units

The following table summarizes activity under the Company’s Restricted Stock Units, or RSU, plans and related information:


	RSUs Outstanding
	Number of Shares (millions)			Weighted-Average Grant Date Fair Value
Unvested — December 31, 2024		5.2		$	53.22
RSUs granted		2.9			41.04
RSUs vested		(1.5	)		56.39
RSUs cancelled		(0.7	)		49.78
Unvested — December 31, 2025		5.9			46.23

The fair value of the RSUs is determined on the grant date based on the fair value of the Company’s common stock. The fair value of the RSUs is recognized as expense ratably over the vesting period of one to four years. The total grant date fair value of the RSUs vested during the years ended December 31, 2025, 2024, and 2023 was $85 million, $63 million, and $55 million, respectively. The aggregate intrinsic value of the shares of the RSUs vested during the years ended December 31, 2025, 2024, and 2023 was $62 million, $54 million, and $33 million, respectively.

Performance Stock Units

The following table summarizes activity under the Company’s Performance Stock Units, or PSUs and related information:


	PSUs Outstanding
	Number of Shares (millions)			Weighted-Average Grant Date Fair Value
Unvested — December 31, 2024		0.6		$	59.39
PSUs granted		0.4			50.77
PSUs vested		(0.2	)		53.44
PSUs cancelled		(0.1	)		49.95
Unvested — December 31, 2025		0.7			57.48

The fair value of the PSUs is determined on the grant date based on the fair value of the Company’s common stock, except for certain PSUs with a market vesting condition, for which fair value is estimated using a Monte Carlo simulation model. PSUs are subject to vest only if certain specified criteria are achieved and the employees’ continued service with the Company. For certain PSUs, the number of PSUs that may vest are also subject to the achievement of certain specified criteria, including both performance conditions and market conditions. As of December 31, 2025, certain specified criteria were deemed probable of achievement or already achieved. Stock-based compensation for PSUs is recognized over the service period beginning in the period the Company determines it is probable that the performance criteria will be achieved. The total grant date fair value of the PSUs vested during the years ended December 31, 2025, 2024, and 2023 was $12 million, $3 million, and $4 million, respectively, with an aggregate intrinsic value of the shares of $9 million, $2 million and $1 million, respectively.

Stock-Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Cost of sales	$	2	$	1	$	1
Research and development		84		87		75
Selling, general and administrative		67		70		59
Total stock-based compensation expense	$	153	$	158	$	135

Stock-based compensation of $2 million, $3 million, and $2 million was capitalized into inventory for the years ended December 31, 2025, 2024, and 2023, respectively. Capitalized stock-based compensation is recognized as cost of sales when the related product is sold.

As of December 31, 2025, the total unrecognized compensation expense related to unvested equity awards, net of estimated forfeitures, was $232 million, which the Company expects to recognize over an estimated weighted-average period of 2 years. In determining the estimated fair value of the stock options, PSOs and ESPP, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine.

Expected Term—The Company’s expected term represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term).

Expected Volatility—The Company’s expected volatility is based on historical volatility over the look-back period corresponding to the expected term.

Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of option.

Expected Dividend—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

Strike price for options awards and PSOs is equal to the closing market value of our common stock on the date of grant.

The fair value of stock option awards granted was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:


	Year Ended December 31,
	2025	2024	2023
Expected term (years)	6	6	6
Expected volatility	53%	55%	55%
Risk-free interest rate	4.1%	4.2%	4.2%
Expected dividend rate	0.0%	0.0%	0.0%

Stock-Based Awards - Summary of the Company's options exercised and vested (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Intrinsic value of options exercised	$ 0	$ 1	$ 5
Cash received from exercise of options	$ 0	$ 6	$ 3
Weighted average estimated fair value of options granted	$ 22.92	$ 29.88	$ 25.53
Estimated fair value of options vested	$ 46	$ 54	$ 60

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Payables and Accruals [Abstract]
Research and clinical study expenses	$ 23	$ 24
Payroll and related expenses	89	94
Revenue related reserves	57	33
Manufacturing and related expenses	67	25
Commercial and development milestones	5	45
Other	24	20
Total accrued liabilities	$ 265	$ 241

Leases (Tables)

12 Months Ended

Dec. 31, 2025

Lessee Disclosure [Abstract]

Summary of Components of Lease Expense

The components of lease expense were as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Operating lease expense	$	12	$	12	$	13
Variable lease expense		5		6		5
Total	$	17	$	18	$	18

Schedule of Maturities of Lease Liabilities and the Reconciliation of Lease Liabilities

The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2025 (in millions):


Year Ending December 31,	Operating
2026	$	15
2027		10
2028		8
2029		7
2030		2
Thereafter		1
Total future lease payments		43
Less: Amount representing interest		(7	)
Present value of future lease payments		36
Less: Lease liabilities, current		(12	)
Lease liabilities, non-current	$	24

Schedule of Weighted Average Remaining Operating Lease Terms and Discount Rates

For the years ended December 31, 2025 and 2024, the weighted-average remaining operating lease terms and the weighted-average discount rates used to determine the lease liability were as follows:


	Year Ended December 31,
	2025			2024
Weighted-average remaining lease term (in years)		4			4
Weighted-average discount rate		10.0	%		10.1	%

Investment in Amlogenyx. Inc. - Changes in the Carrying Value of Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Investments, All Other Investments [Abstract]
Beginning Balance	$ 7	$ 0
Issuance of equity from noncontrolling interest		7
Changes and adjustments	0
Ending Balance	$ 7	$ 7

- Definition

Carrying amount, attributable to parent and noncontrolling interests, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

+ References

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-Name Accounting Standards Codification
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+ Details

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (575)	$ (569)	$ (607)
Other comprehensive income (loss):
Foreign currency translation adjustments	3	(2)	0
Change in unrealized gain on available-for-sale securities	1	0	8
Other comprehensive income (loss):	2	(2)	8
Total comprehensive loss	$ (573)	$ (571)	$ (599)

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

- Definition

Amount after tax, before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

+ References + Details

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

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+ Details

Income Taxes - Components of Company's Income Tax Provision (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Current provision for income taxes:
State			$ (3)
International	$ 4	$ 3	3
Total current tax provision	4	3
Deferred tax provision:
State			(2)
International		(1)
Total deferred tax benefit		(1)	(2)
Total provision for (benefit from) income taxes	$ 4	$ 2	$ (2)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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+ Details

Net Loss per Share - Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Options to Purchase Common Stock, RSUs, and PSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	16.8	14.2	16.3

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash


	December 31,
	2025		2024		2023
Cash and cash equivalents	$	421	$	174	$	214
Restricted cash included in other current assets		13		7		2
Restricted cash included in other non-current assets		2		3		3
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	436	$	184	$	219

Income Taxes - Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Loss carryforwards	$ 511	$ 309
Tax credits	426	370
Stock options	46	52
Accruals and reserves	34	32
Fixed assets and intangibles	26	32
Liabilities for sales of future royalties	276	197
Basis difference in equity investments	8	9
Capitalized research and development costs	34	212
Other	0	1
Gross deferred tax assets	1,361	1,214
Valuation allowance	(1,355)	(1,207)
Total deferred tax assets	6	7
Deferred tax liabilities:
Gross deferred tax liabilities	(35)	(36)
Net deferred tax liabilities	(29)	(29)
Right-of-use Lease Assets
Deferred tax liabilities:
Gross deferred tax liabilities	(5)	(6)
In-process Research and Development [Member]
Deferred tax liabilities:
Gross deferred tax liabilities	$ (30)	$ (30)

Liabilities for Sales of Future Royalties (Tables)

12 Months Ended

Dec. 31, 2025

Deferred Revenue Disclosure [Abstract]

Schedule of Activity Within Liability for Sale of Future Royalties

The following table shows the activity within the liability account (in millions):



	Liabilities for Sales of Future Royalties
	RPI			OMERS 2022			OMERS 2025		Total
December 31, 2023	$	377		$	515		$	—	$	892
Royalty revenue		(26	)		(59	)		—		(85	)
Non-cash interest expense		24			39			—		63
December 31, 2024		375			495			—		870
Net proceeds from sale of future royalties		—			—			392		392
Royalty revenue		(29	)		(79	)		—		(108	)
Non-cash interest expense		20			36			6		62
December 31, 2025	$	366		$	452		$	398	$	1,216

Stock-Based Awards - Fair Value of Stock Option Awards Granted Estimated Using Black-Scholes Option-Pricing Model (Details) - Stock Options	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 years	6 years	6 years
Expected volatility	53.00%	55.00%	55.00%
Risk-free interest rate	4.10%	4.20%	4.20%
Expected dividend rate	0.00%	0.00%	0.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Leases - Schedule of Weighted Average Remaining Operatiing Lease Terms and Discount Rates (Details)	Dec. 31, 2025	Dec. 31, 2024
Lease, Cost [Abstract]
Weighted-average remaining lease term (in years)	4 years	4 years
Weighted-average discount rate	10.00%	10.10%

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2025 USD ($) Segment	Dec. 31, 2024 USD ($)
Accounting Policies [Abstract]
Number of reportable segments \| Segment	1
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]	srt:ChiefExecutiveOfficerMember
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description	The Company’s Chief Operating Decision Maker, or CODM, is the Company's Chief Executive Officer. The CODM manages the Company’s operations on an integrated basis for the purpose of allocating resources. When evaluating the Company’s financial performance, the CODM regularly reviews total revenues and total expenses and makes decisions using this information on a consolidated basis.
Credit losses recorded for receivables	$ 0	$ 0
Unrecognized tax benefits related to interest or penalties	$ 0

Subsequent Events Additional Information (Details) - Subsequent Event [Member] $ in Millions	1 Months Ended
	Feb. 28, 2026 USD ($)
Subsequent Event [Line Items]
Restructuring plan, workforce reduction percentage	10.00%
Expected termination and severance costs	$ 50

License and Research Agreements - Share of Collaboration and Royalty Revenue Related to Crysvita (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 673	$ 560	$ 434
Royalty revenue
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	304	275	183
Royalty revenue \| Kyowa Kirin Collaboration \| Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	192	174	113
Collaboration Revenue \| Kyowa Kirin Collaboration \| Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	0	0	70
Non-cash royalty revenue \| Kyowa Kirin Collaboration \| Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	83	75	49
Non-cash royalty revenue \| Kyowa Kirin Collaboration \| Royalty Revenue in European Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	29	26	21
Collaboration and Royalty \| Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	481	410	328
Collaboration and Royalty \| Kyowa Kirin Collaboration \| Profit Share Territory
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	275	249	232
Product sales
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	369	285	180
Product sales \| Kyowa Kirin Collaboration
Disaggregation Of Revenue [Line Items]
Collaboration and license revenue	$ 177	$ 135	$ 75

Pay vs Performance Disclosure - USD ($) $ in Millions	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (575)	$ (569)	$ (607)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Balance Sheet Components - Summary of Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 380	$ 378
Less accumulated depreciation	(136)	(112)
Property, plant and equipment, net	244	266
Building
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 182	$ 182
Building \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	20 years	20 years
Building \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	30 years	30 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 55	$ 58
Property, plant and equipment, estimated useful lives	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember
Research and Development Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 65	$ 60
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 7	$ 6
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 16	$ 16
Computer Equipment and Software \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	3 years	3 years
Computer Equipment and Software \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 37	$ 37
Manufacturing Equipment \| Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	5 years	5 years
Manufacturing Equipment \| Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives (years)	15 years	15 years
Land
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 17	$ 17
Other
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 1	$ 2

Investment in Amlogenyx. Inc.

12 Months Ended

Dec. 31, 2025

Investments, All Other Investments [Abstract]

Investment in Amlogenyx. Inc.

Investment in Amlogenyx Inc.

In July 2024, the Company contributed certain intellectual property rights to Amlogenyx Inc., or Amlogenyx, a subsidiary of the Company, and received 9.0 million shares of common stock of Amlogenyx. A third-party investor along with one of its affiliated entities, and the Company, each contributed $7 million to Amlogenyx and in exchange, each received approximately 1.6 million shares of series seed preferred stock of Amlogenyx. The purpose of Amlogenyx is to pursue the application of the Company’s novel adeno-associated virus, or AAV, gene therapy to treat beta-amyloid disorders and related neurodegenerative diseases.

Amlogenyx was determined to be a VIE and the Company is the primary beneficiary as it has the power to direct the activities that would most significantly impact the economic performance of Amlogenyx, including the performance of R&D activities relating to its sole product candidate. As the primary beneficiary, the Company has consolidated the financial position, results of operations and cash flows of Amlogenyx in its financial statements and all intercompany balances have been eliminated in consolidation. Upon initial consolidation, the non-controlling interest of the third-party investor was recorded at its estimated fair value of $7.0 million, which is equal to their original investment.

As of December 31, 2025 and 2024, total assets included on the Consolidated Balance Sheets for Amlogenyx were $5 million and $14 million, respectively. The assets primarily consisted of cash and cash equivalents which may only be used to settle obligations of Amlogenyx.

Noncontrolling interest related to the third-party investment in Amlogenyx is reported on the Consolidated Balance Sheets in mezzanine equity.

Changes in the carrying value of noncontrolling interest for the year ended December 31, 2025, were as follows (in millions):


	Noncontrolling Interest
As of December 31, 2023	$	—
Issuance of equity from noncontrolling interest		7
As of December 31, 2024	$	7
Changes and adjustments		—
As of December 31, 2025	$	7

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues:
Total revenues	$ 673	$ 560	$ 434
Operating expenses:
Cost of sales	109	77	45
Research and development	750	698	648
Selling, general and administrative	349	321	310
Total operating expenses	1,208	1,096	1,003
Loss from operations	(535)	(536)	(569)
Interest income	25	37	27
Non-cash interest expense on liabilities for sales of future royalties	(62)	(63)	(66)
Other income (expense)	1	(5)	(1)
Loss before income taxes	(571)	(567)	(609)
(Provision for) benefit from income taxes	(4)	(2)	2
Net loss	$ (575)	$ (569)	$ (607)
Net loss per share, basic	$ (5.83)	$ (6.29)	$ (8.25)
Net loss per share, diluted	$ (5.83)	$ (6.29)	$ (8.25)
Shares used in computing net loss per share, Basic	98.6	90.5	73.5
Shares used in computing net loss per share, Diluted	98.6	90.5	73.5
Product sales
Revenues:
Total revenues	$ 369	$ 285	$ 180
Royalty revenue
Revenues:
Total revenues	304	275	183
Collaboration and license
Revenues:
Total revenues	$ 0	$ 0	$ 71

Intangible Assets, net (Table)

12 Months Ended

Dec. 31, 2025

Intangible Assets, Net (Excluding Goodwill) [Abstract]

Summary of Company's Intangible Assets

The Company's intangible assets were as follows (in millions, except for years):


	December 31, 2025
	Gross Carrying Amount		Weighted-Average Life (Years)		Accumulated Amortization			Net Carrying Amount
Indefinite-lived intangibles	$	129		—	$	—		$	129
Finite-lived intangibles		68		9		(21	)		47
Total intangible assets	$	197		—	$	(21	)	$	176


	December 31, 2024
	Gross Carrying Amount		Weighted-Average Life (Years)		Accumulated Amortization			Net Carrying Amount
Indefinite-lived intangibles	$	129		—	$	—		$	129
Finite-lived intangibles		62		9		(13	)		49
Total intangible assets	$	191		—	$	(13	)	$	178

Schedule of Expected Amortization of the Intangible Assets

The expected amortization of intangible assets, as of December 31, 2025, for each of the next five years and thereafter is as follows (in millions):


2026	$	8
2027		7
2028		7
2029		7
2030		7
Thereafter		11
Total	$	47

Fair Value Measurements

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Fair Value Measurements

Certain financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. The carrying amounts of liabilities for the sales of future royalties also approximate their fair value. Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

The Company’s financial instruments consist of Level 1, Level 2, and Level 3 assets. Where quoted prices are available in an active market, securities are classified as Level 1. Money market funds and U.S. Government treasury bills are classified as Level 1. Level 2 assets consist primarily of corporate bonds, asset backed securities, commercial paper, U.S. Government Treasury and agency securities, and debt securities in government-sponsored entities based upon quoted market prices for similar movements in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third-party data providers, including but not limited to, benchmark yields, interest rate curves, reported trades, broker/dealer quotes and reference data.

The Company determines the fair value of its equity investment in Solid Biosciences, Inc., or Solid, by using the quoted market prices, which are Level 1 fair value measurements.

The following tables set forth the fair value of the Company’s financial assets and liabilities remeasured on a recurring basis based on the three-tier fair value hierarchy (in millions):


	December 31, 2025
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	320	$	—	$	—	$	320
Time deposits		—		10		—		10
Corporate bonds		—		263		—		263
Commercial paper		—		37		—		37
U.S. Government Treasury and agency securities		12		23		—		35
Investment in Solid common stock		3		—		—		3
Deferred compensation assets		—		19		—		19
Total financial assets	$	335	$	352	$	—	$	687

Financial Liabilities:
Deferred compensation liabilities	$	—	$	19	$	—	$	19


	December 31, 2024
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	114	$	—	$	—	$	114
Time deposits		—		10		—		10
Corporate bonds		—		392		—		392
Commercial paper		—		21		—		21
U.S. Government Treasury and agency securities		—		159		—		159
Investment in Solid common stock		2		—		—		2
Deferred compensation assets		—		15		—		15
Total financial assets	$	116	$	597	$	—	$	713

Financial Liabilities:
Deferred compensation liabilities	$	—	$	16	$	—	$	16

Deferred compensation liabilities consist of short-term liabilities of $1 million and $1 million as of December 31, 2025 and 2024, respectively, included in accrued liabilities on the Consolidated Balance Sheets, and long-term liabilities of $18 million and $15 million as of December 31, 2025 and 2024, respectively, included in other non-current liabilities on the Consolidated Balance Sheets. There have been no material net gains or losses on deferred compensation assets or liabilities for the periods presented.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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+ Details

Revenue

12 Months Ended

Dec. 31, 2025

Revenue from Contract with Customer [Abstract]

Revenue

The following table disaggregates total revenues from external customers by product sales, royalty revenue, and collaboration and license revenue (in millions):


	Year Ended December 31,
	2025		2024		2023
Product sales:
Crysvita	$	177	$	135	$	75
Dojolvi		96		88		71
Evkeeza		59		32		4
Mepsevii		37		30		30
Total product sales		369		285		180
Crysvita royalty revenue		304		275		183
Collaboration and license revenue:
Crysvita collaboration revenue in Profit-Share Territory		—		—		70
Other		—		—		1
Total collaboration and license revenue		—		—		71
Total revenues	$	673	$	560	$	434

The following table disaggregates total revenues based on geographic location (in millions):


	Year Ended December 31,
	2025		2024		2023
North America	$	377	$	340	$	307
Latin America		170		131		77
Europe, Middle East, and Africa		108		80		48
Asia-Pacific		18		9		2
Total revenues	$	673	$	560	$	434

The following table presents the activity and ending balances for product sales related accruals and allowances (in millions):


	Year Ended December 31,
	2025			2024			2023
Balance of product sales reserve at beginning of year	$	33		$	17		$	11
Provisions		50			38			19
Payments		(30	)		(21	)		(13	)
Adjustments		4			(1	)		—
Balance of product sales reserve at end of year	$	57		$	33		$	17

The Company’s largest accounts receivable balance was from a collaboration partner, KKC, and was 62% and 70% of the total accounts receivable balance as of December 31, 2025 and 2024, respectively.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Subsequent Event

12 Months Ended

Dec. 31, 2025

Subsequent Events [Abstract]

Subsequent Event

19.

Subsequent Events

In February 2026, the Company’s Board of Directors approved a strategic restructuring plan that includes a reduction of approximately 10% of the Company’s workforce, or the Restructuring Plan. As a result of this reduction in force, the Company estimates that it will incur restructuring charges of approximately $50 million in total in connection with employee related termination and severance costs, charges for the termination of UX143 manufacturing agreements, and other related activities,

substantially all of which are expected to be recognized during the first half of 2026. Cash payments related to these costs are expected to be made over the same period.

The Restructuring Plan is intended to reduce the Company's headcount and expenses by focusing resources on the Company’s largest value drivers. Management’s estimates are based on information available as of the approval date of the Restructuring Plan and are subject to change as the plan is implemented.

Liabilities for Sales of Future Royalties - Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	$ 870	$ 892
Net proceeds from sale of future royalties	392	0	$ 0
Royalty revenue	(108)	(85)
Non-cash interest expense	62	63
Liability for sale of future royalties at end of year	1,216	870	892
RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	375	377
Net proceeds from sale of future royalties	0
Royalty revenue	(29)	(26)
Non-cash interest expense	20	24
Liability for sale of future royalties at end of year	366	375	377
2022 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	495	515
Net proceeds from sale of future royalties	0
Royalty revenue	(79)	(59)
Non-cash interest expense	36	39
Liability for sale of future royalties at end of year	452	495	515
2025 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Liability for sale of future royalties at beginning of year	0	0
Net proceeds from sale of future royalties	392
Royalty revenue	0	0
Non-cash interest expense	6	0
Liability for sale of future royalties at end of year	$ 398	$ 0	$ 0

Income Taxes

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

Income Taxes

14.

Income Taxes

The components of the Company’s loss before income taxes were as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Domestic	$	565	$	563	$	609
Foreign		6		4		—
Total loss before income taxes	$	571	$	567	$	609

The components of the Company’s income tax provision (benefit) were as follows (in millions):


	Year Ended December 31,
	2025		2024			2023
Current provision for income taxes:
Federal	$	—	$	—		$	—
State		—		—			(3	)
International		4		3			3
Total current tax provision		4		3			—
Deferred tax provision:
Federal		—		—			—
State		—		—			(2	)
International		—		(1	)		—
Total deferred tax benefit		—		(1	)		(2	)
Total provision for (benefit from) income taxes	$	4	$	2		$	(2	)

The Company has incurred net operating losses since inception. The Company has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.

For the year ended December 31, 2023, the Company recognized an income tax benefit of $5 million attributable to modifications in its state apportionment methodology, offset by an income tax expense of $3 million from foreign jurisdictions. For the year ended December 31, 2024, the Company recognized income tax expense of $1 million from foreign jurisdictions alongside a nominal amount of state tax. For the year ended December 31, 2025, the Company recognized income tax expense of $4 million from foreign jurisdictions and a nominal amount of state tax. The Company realized no benefit for current year losses due to a full valuation allowance against the U.S. net deferred tax assets.

The table below provides the updated requirements of ASU 2023-09 for the year ended December 31, 2025.

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows (in millions except percentage amounts):


	Year Ended December 31,
	2025
Federal statutory income tax rate	$	(120	)	21.0		%
State income taxes, net of federal benefit (1)		—		—
Foreign tax effects		5		(0.9	)
Effect of changes in tax laws or rates enacted in the current period		—		—
Effect of cross-border tax laws		5		(0.9	)
Tax credits		—		—
Research tax credit		(12	)	2.1
Orphan drug credit		(32	)	5.6
Change in valuation allowance		145		(25.4	)
Nontaxable or nondeductible items
Share-based payment awards		14		(2.5	)
Other		(1	)	0.3
Uncertain tax positions		—		—
Other Adjustments		—		—
Provision for income taxes	$	4		(0.7	)	%
(1) Includes a nominal amount of state tax. Illinois State tax made up the majority (greater than 50 percent) of the tax effect in this category.

As previously disclosed for the years ended December 31, 2024 and 2023, prior to the adoption of ASU 2023-09, the effective income tax rate differs from the statutory federal income tax rate as follows:


	Year Ended December 31,
	2024				2023
Federal statutory income tax		21.0		%		21.0		%
State income taxes, net of federal benefit		—				0.8
Federal tax credits		10.8				7.3
Other		0.1				(0.7	)
Nondeductible permanent items		(1.1	)			(0.3	)
Stock-based compensation		(1.6	)			(1.8	)
Uncertain tax positions		(2.0	)			(1.4	)
Change in valuation allowance		(27.1	)			(24.1	)
Foreign rate differential		(0.4	)			(0.5	)
Provision for income taxes		(0.3	)	%		0.3		%

Income taxes paid (net of refunds) for the year ended December 31, 2025 is disaggregated as follows (in millions):


	Year Ended December 31,
	2025
Federal income taxes paid (net of refunds)	$	—
State income taxes paid (net of refunds)		—
Foreign income taxes paid (net of refunds)
Brazil		1
Mexico		1
Other (1)		2
Total income taxes paid (net of refunds)	$	4
(1) There was a nominal amount of foreign taxes paid (net of refunds) to Canada, Switzerland, France, Japan, and the Netherlands.

The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in millions):


	Year Ended December 31,
	2025			2024
Deferred tax assets:
Loss carryforwards	$	511		$	309
Tax credits		426			370
Stock options		46			52
Accruals and reserves		34			32
Fixed assets and intangibles		26			32
Liabilities for sales of future royalties		276			197
Basis difference in equity investments		8			9
Capitalized research and development costs		34			212
Other		—			1
Gross deferred tax assets		1,361			1,214
Valuation allowance		(1,355	)		(1,207	)
Total deferred tax assets		6			7
Deferred tax liabilities:
In-process research and development		(30	)		(30	)
Right-of-use lease assets		(5	)		(6	)
Gross deferred tax liabilities		(35	)		(36	)
Net deferred tax liabilities	$	(29	)	$	(29	)

As of December 31, 2025 and 2024, the Company had approximately $2,104 million and $1,191 million, respectively, of federal net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2031. As of December 31, 2025 and 2024, the Company had approximately $936 million and $744 million, respectively, of state net operating loss carryforwards available to reduce future taxable income that will begin to expire in 2031.

As of December 31, 2025 and 2024, the Company had federal research tax credit carryforwards of approximately $60 million and $45 million, respectively, available to reduce future tax liabilities that will begin to expire in 2031. As of December 31, 2025 and 2024, the Company had state research credit carryforwards of $110 million and $92 million, respectively, available to reduce future tax liabilities. The majority of these credits will be carried forward indefinitely, and others will expire at various dates in the future.

As of December 31, 2025 and 2024, the Company had federal Orphan Drug Credits of approximately $379 million and $339 million, respectively, available to reduce future tax liabilities that will begin to expire in 2031.

The Company’s ability to use net operating loss and tax credit carryforwards to reduce future taxable income and liabilities may be subject to annual limitations pursuant to Internal Revenue Code Sections 382 and 383 as a result of ownership changes in the past and future. As a result of ownership changes in 2012 and 2011, $4 million of federal net operating loss carryforwards, $4 million of state net operating loss carryforwards, and a nominal amount of federal tax credits are permanently limited. Deferred tax assets for net operating losses and tax credits have been reduced and a corresponding adjustment to the valuation allowance has been recorded.

The valuation allowance increased by $148 million and $171 million during the years ended December 31, 2025 and 2024, respectively.

The Company recorded unrecognized tax benefits for uncertainties in income taxes. A reconciliation of the Company’s unrecognized tax benefits follows (in millions):


	December 31,
	2025			2024		2023
Balance at beginning of year	$	97		$	80	$	67
Additions based on tax positions related to current year		15			15		12
Additions for tax positions of prior years		—			2		1
Reductions for tax positions of prior years		(1	)		—		—
Balance at end of year	$	111		$	97	$	80

Approximately $1 million in unrecognized tax benefits would impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. For the years ended December 31, 2025, 2024 and 2023, the Company recognized nominal amounts for accrued interest and penalties as a component of income tax expense. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next year.

It is the Company’s intention to reinvest the earnings of its non-U.S. subsidiaries in their operations. As of December 31, 2025, the Company had not made a provision for any incremental foreign withholding taxes on approximately $17 million of the excess of the amount of net income for financial reporting over the tax basis of investments in foreign subsidiaries that are essentially permanent in duration. If these earnings were repatriated to the U.S., the deferred tax liability associated with these temporary differences would result in a nominal amount of withholding taxes.

The Company files income tax returns in the U.S. federal, 40 state tax jurisdictions, and ten foreign countries. The federal and state income tax returns from inception to December 31, 2025 remain subject to examination.

- Definition

The entire disclosure for income tax.

+ References

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+ Details

Stock-Based Awards- Summary Activity Under the Performance Stock Option (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vested and exercisable December 31, 2025	6.5
Vested and expected to vest December 31, 2025	8.7
Weighted- Average Exercise Price,Weighted Average Exercise Price	$ 66.31
Weighted Average Exercise Price, Vested and expected to vest December 31, 2025	$ 61.24
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2025	6 years
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2025	5 years
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2025	$ 0
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2025	$ 0
Performance Stock Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance	1.2
PSOs cancelled	(0.4)
Outstanding, Number of Shares, Unvested, Ending Balance	0.8	1.2
Vested and exercisable December 31, 2025	0.8
Vested and expected to vest December 31, 2025	0.8
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance	$ 67.37
Weighted Average Exercise Price ,PSOs cancelled	67.37
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Ending Balance	67.37	$ 67.37
Weighted- Average Exercise Price,Weighted Average Exercise Price	67.37
Weighted Average Exercise Price, Vested and expected to vest December 31, 2025	$ 67.37
Weighted-Average Remaining Contractual Term,Outstanding at December 31, 2025	1 year	2 years
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2025	1 year
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2025	1 year
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2025	0
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2025	$ 0

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Schedule Of Available For Sale Securities [Line Items]
Depreciation expense	$ 27	$ 30	$ 22
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities remaining contractual maturities	2 years

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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+ Details

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

Components of Company's Loss Before Income Taxes

The components of the Company’s loss before income taxes were as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Domestic	$	565	$	563	$	609
Foreign		6		4		—
Total loss before income taxes	$	571	$	567	$	609

Components of Company's Income Tax Provision (Benefit)

The components of the Company’s income tax provision (benefit) were as follows (in millions):


	Year Ended December 31,
	2025		2024			2023
Current provision for income taxes:
Federal	$	—	$	—		$	—
State		—		—			(3	)
International		4		3			3
Total current tax provision		4		3			—
Deferred tax provision:
Federal		—		—			—
State		—		—			(2	)
International		—		(1	)		—
Total deferred tax benefit		—		(1	)		(2	)
Total provision for (benefit from) income taxes	$	4	$	2		$	(2	)

Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows (in millions except percentage amounts):


	Year Ended December 31,
	2025
Federal statutory income tax rate	$	(120	)	21.0		%
State income taxes, net of federal benefit (1)		—		—
Foreign tax effects		5		(0.9	)
Effect of changes in tax laws or rates enacted in the current period		—		—
Effect of cross-border tax laws		5		(0.9	)
Tax credits		—		—
Research tax credit		(12	)	2.1
Orphan drug credit		(32	)	5.6
Change in valuation allowance		145		(25.4	)
Nontaxable or nondeductible items
Share-based payment awards		14		(2.5	)
Other		(1	)	0.3
Uncertain tax positions		—		—
Other Adjustments		—		—
Provision for income taxes	$	4		(0.7	)	%
(1) Includes a nominal amount of state tax. Illinois State tax made up the majority (greater than 50 percent) of the tax effect in this category.


	Year Ended December 31,
	2024				2023
Federal statutory income tax		21.0		%		21.0		%
State income taxes, net of federal benefit		—				0.8
Federal tax credits		10.8				7.3
Other		0.1				(0.7	)
Nondeductible permanent items		(1.1	)			(0.3	)
Stock-based compensation		(1.6	)			(1.8	)
Uncertain tax positions		(2.0	)			(1.4	)
Change in valuation allowance		(27.1	)			(24.1	)
Foreign rate differential		(0.4	)			(0.5	)
Provision for income taxes		(0.3	)	%		0.3		%

Schedule of Income Taxes Paid (Net of Refunds)

Income taxes paid (net of refunds) for the year ended December 31, 2025 is disaggregated as follows (in millions):


	Year Ended December 31,
	2025
Federal income taxes paid (net of refunds)	$	—
State income taxes paid (net of refunds)		—
Foreign income taxes paid (net of refunds)
Brazil		1
Mexico		1
Other (1)		2
Total income taxes paid (net of refunds)	$	4
(1) There was a nominal amount of foreign taxes paid (net of refunds) to Canada, Switzerland, France, Japan, and the Netherlands.

Schedule of Tax Effect of Temporary Differences to Significant Portions of Deferred Tax Assets

The tax effect of temporary differences that give rise to significant portions of the deferred tax assets is presented below (in millions):


	Year Ended December 31,
	2025			2024
Deferred tax assets:
Loss carryforwards	$	511		$	309
Tax credits		426			370
Stock options		46			52
Accruals and reserves		34			32
Fixed assets and intangibles		26			32
Liabilities for sales of future royalties		276			197
Basis difference in equity investments		8			9
Capitalized research and development costs		34			212
Other		—			1
Gross deferred tax assets		1,361			1,214
Valuation allowance		(1,355	)		(1,207	)
Total deferred tax assets		6			7
Deferred tax liabilities:
In-process research and development		(30	)		(30	)
Right-of-use lease assets		(5	)		(6	)
Gross deferred tax liabilities		(35	)		(36	)
Net deferred tax liabilities	$	(29	)	$	(29	)

Unrecognized Tax Benefits

A reconciliation of the Company’s unrecognized tax benefits follows (in millions):


	December 31,
	2025			2024		2023
Balance at beginning of year	$	97		$	80	$	67
Additions based on tax positions related to current year		15			15		12
Additions for tax positions of prior years		—			2		1
Reductions for tax positions of prior years		(1	)		—		—
Balance at end of year	$	111		$	97	$	80

Investment in Amlogenyx. Inc. (Tables)

12 Months Ended

Dec. 31, 2025

Investments, All Other Investments [Abstract]

Changes in the Carrying Value of Noncontrolling Interest

Changes in the carrying value of noncontrolling interest for the year ended December 31, 2025, were as follows (in millions):


	Noncontrolling Interest
As of December 31, 2023	$	—
Issuance of equity from noncontrolling interest		7
As of December 31, 2024	$	7
Changes and adjustments		—
As of December 31, 2025	$	7

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2012
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ 4	$ 3
Deferred tax assets net operating loss, federal tax credits				$ 4
Deferred tax assets net operating loss carryforwards	511	309
Valuation allowance increased	148	171
Effective income tax rate unrecognized tax benefits	1
Undistributed earnings of foreign subsidiaries	17
Federal
Tax Credit Carryforward [Line Items]
Deferred tax assets operating loss carryforwards subject to expiration	$ 2,104	1,191
Operating loss carryforwards expiration year	2031
Tax credit carryforwards	$ 60	45
Tax credit carryforwards expiration year	2031
Deferred tax assets net operating loss carryforwards				4
Federal \| Orphan Drug Credits [Member]
Tax Credit Carryforward [Line Items]
Deferred tax assets operating loss carryforwards subject to expiration	$ 379	339
Operating loss carryforwards expiration year	2031
State
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ 4	1	$ 5
Deferred tax assets operating loss carryforwards subject to expiration	$ 936	744
Operating loss carryforwards expiration year	2031
Tax credit carryforwards	$ 110	92
Deferred tax assets net operating loss carryforwards				$ 4
International
Tax Credit Carryforward [Line Items]
Current state income tax expense	$ 4	$ 1	$ 3

Balance Sheet Components - Summary of Cash Equivalents and Marketable Debt Securities Classified as Available For Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 665	$ 695
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Value	665	696
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	320	114
Estimated Fair Value	320	114
Time Deposits
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10	10
Estimated Fair Value	10	10
Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	263	391
Gross Unrealized Gains		1
Gross Unrealized Losses	0
Estimated Fair Value	263	392
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	37	21
Estimated Fair Value	37	21
U.S. Government Treasury and Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	35	159
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 35	$ 159

Commitments and Contingencies

12 Months Ended

Dec. 31, 2025

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

15.

Commitments and Contingencies

The Company has various manufacturing, clinical, research, and other contracts with vendors in the conduct of the normal course of its business. Other than as noted below, contracts are terminable, with varying provisions regarding termination. If a contract with a specific vendor were to be terminated, the Company would only be obligated for the products or services that the Company had received at the time the termination became effective.

Manufacturing and service contract obligations primarily relate to manufacturing of product for our clinical stage pipeline, the majority of which are due in the next 12 months.

The terms of certain of the Company’s licenses, royalties, development and collaboration agreements, as well as other research and development activities, require the Company to pay potential future milestone payments based on product development success. The amount and timing of such obligations are unknown or uncertain. These potential obligations are further described in “Note 8. License and Research Agreements.”

See “Note 9. Leases” for lease commitments.

Contingencies

In the ordinary course of business, the Company may become party to various claims and complaints. See “Item 3. Legal Proceedings” for material legal proceedings the Company is aware of. The process of resolving matters through litigation or other means is inherently uncertain, however management does not believe that any ultimate liability resulting from any of these potential claims will have a material adverse effect on its results of operations, financial position, or liquidity.

Guarantees and Indemnifications

The Company indemnifies each of its directors and officers for certain events or occurrences, subject to certain limits, while the director or officer is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as a director or officer may be subject to any proceeding arising out of acts or omissions of such director and officer in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director liability insurance. This insurance allows the transfer of risk associated with the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, it has not recognized any liabilities relating to these obligations for any period presented.

Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Jun. 30, 2024	Feb. 29, 2024	Oct. 31, 2023	May 31, 2021	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Stockholders Equity [Line Items]
Stock sold in at-the-market offering							1,200,000
Net proceeds from at-the-market offering					$ 80	$ 0	$ 53
Pre Funded Warrant
Stockholders Equity [Line Items]
Underwritten Public Offering Shares						1,500,000
Number of warrants exercised					0
Open Market Sale
Stockholders Equity [Line Items]
Option to sell common stock aggregate offering price		$ 350		$ 350
At-the-Market Offerings
Stockholders Equity [Line Items]
Common stock shares sold					2,200,000
Underwritten Public Offering
Stockholders Equity [Line Items]
Common stock shares sold	8,800,000		9,800,000
Shares purchased by underwriters	1,300,000		1,500,000
Public offering price	$ 39		$ 30
Underwritten Public Offering \| Pre Funded Warrant
Stockholders Equity [Line Items]
Underwritten Public Offering Shares	1,500,000		1,700,000
Pre-funded warrant price	$ 38.999		$ 29.999
Common stock warrants, exercise price	$ 0.001		$ 0.001
Net proceeds from sale of common stock	$ 381		$ 327

Fair Value Measurements - Summary of Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 687	$ 713
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	335	116
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	352	597
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	320	114
Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	320	114
Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10	10
Time Deposits \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	10	10
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	263	392
Corporate Bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	263	392
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	37	21
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	37	21
U.S. Government Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	35	159
U.S. Government Treasury and Agency Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	12
U.S. Government Treasury and Agency Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	23	159
Investments in Solid Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	3	2
Investments in Solid Common Stock \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	3	2
Deferred compensation assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	19	15
Deferred compensation assets \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	19	15
Deferred compensation liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	19	16
Deferred compensation liabilities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value	$ 19	$ 16

Liabilities for Sales of Future Royalties - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Nov. 30, 2025	Jul. 31, 2022	Dec. 31, 2019	Dec. 31, 2025
2022 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Profit loss sharing percentage on net sales	30.00%	30.00%
2025 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Royalty repurchase option description	Under the agreement, OMERS granted the Company an option to repurchase the entire purchased interest, that expires in November 2027, for 1.35 times the purchase price, or $540 million
Share repurchase expiration date	Nov. 30, 2027
Royalty repurchase amount	$ 540.0
Profit loss sharing percentage on net sales	25.00%
Royalty Purchase Agreement \| RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties			$ 320.0
Royalty payment termination description				The agreement with RPI will automatically terminate, and the payment of royalties to RPI will cease, in the event aggregate royalty payments received by RPI are equal to or greater than $608.0 million prior to December 31, 2030, or in the event aggregate royalty payments received by RPI are less than $608 million prior to December 31, 2030, or when aggregate royalty payments received by RPI are equal to $800 million.
Royalties transaction costs net			$ 6.0
Effective annual interest rate				5.50%
Non-cash collaboration royalty revenue				$ 128.0
Royalty Purchase Agreement \| 2022 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties		$ 500.0
Royalty payment termination description		In July 2022, the Company entered into a Royalty Purchase Agreement with OMERS, or the 2022 OMERS Agreement. Pursuant to the agreement, OMERS paid $500 million to the Company in consideration for the right to receive 30% of the future royalty payments due to the Company from KKC based on net sales of Crysvita in the U.S. and Canada under the terms of the KKC Collaboration Agreement. The calculation of royalty payments to OMERS is based on net sales of Crysvita beginning in April 2023 and will expire upon the earlier of the date on which aggregate payments received by OMERS equals $725 million or on the date the final royalty payment is made to the Company under the KKC Collaboration Agreement.
Royalty agreement termination threshold amount	$ 725.0	$ 725.0
Payment from sale of future royalties		500.0
Royalties transaction costs net		$ 9.0
Effective annual interest rate				7.30%
Non-cash collaboration royalty revenue				$ 206.0
Royalty Purchase Agreement \| 2025 OMERS Agreement
Liability For Sale Of Future Royalties [Line Items]
Proceeds from sale of future royalties	400.0
Royalty agreement termination threshold amount	620.0
Payment from sale of future royalties	400.0
Royalties transaction costs net	$ 8.0
Effective annual interest rate				0.20%
Non-cash collaboration royalty revenue				$ 0.0
Royalty Purchase Agreement \| Minimum \| RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount				608.0
Royalty Purchase Agreement \| Maximum \| RPI Finance Trust (RPI)
Liability For Sale Of Future Royalties [Line Items]
Royalty agreement termination threshold amount				$ 800.0

Commitments and Contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2025
Manufacturing and Services
Commitments And Contingencies Disclosure Line Items
Contractual Obligation Maturity Period	12 months

Accumulated Other Comprehensive (Loss) Income

12 Months Ended

Dec. 31, 2025

Other Comprehensive Income (Loss), Net of Tax [Abstract]

Accumulated Other Comprehensive (Loss) Income

18.

Accumulated Other Comprehensive Income (Loss)

Total accumulated other comprehensive income (loss) consisted of the following (in millions):


	Year Ended December 31,
	2025		2024
Cumulative foreign currency translation adjustment	$	1	$	(2	)
Unrealized gain on securities available-for-sale		—		1
Total accumulated other comprehensive income (loss)	$	1	$	(1	)

19.

Subsequent Events

substantially all of which are expected to be recognized during the first half of 2026. Cash payments related to these costs are expected to be made over the same period.

Revenue - Additional Information (Details)	Dec. 31, 2025	Dec. 31, 2024
Customer One
Disaggregation of Revenue [Line Items]
Percentage of gross accounts receivable balance	62.00%	70.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Stock-Based Awards - Summary of Activity Under Stock Option Plans Including 2011 Plan and 2014 Plan and 2023 Plan (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Number of Options, Outstanding, Beginning Balance	9.4
Number of Options, Options granted	1.2
Number of Options, Options exercised	0.0
Number of Options, Options cancelled	(1.7)
Number of Options, Outstanding, Ending Balance	8.9	9.4
Vested and exercisable December 31, 2025	6.5
Vested and expected to vest December 31, 2025	8.7
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 65.54
Weighted Average Exercise Price, Options granted	41.75
Weighted Average Exercise Price, Options exercised	38.57
Weighted Average Exercise Price, Options cancelled	73.53
Weighted Average Exercise Price, Outstanding, Ending Balance	60.87	$ 65.54
Weighted- Average Exercise Price,Weighted Average Exercise Price	66.31
Weighted Average Exercise Price, Vested and expected to vest December 31, 2025	$ 61.24
Weighted Average Remaining Contractual Term (Years), Outstanding	6 years	6 years
Weighted Average Remaining Contractual Term (Years), Vested and exercisable - December 31, 2025	5 years
Weighted-Average Remaining Contractual Term,Vested and expected to vest December 31, 2025	6 years
Aggregate Intrinsic Value, Outstanding	$ 0	$ 2
Aggregate Intrinsic Value, Vested and exercisable - December 31, 2025	0
Aggregate Intrinsic Value, Vested and expected to vest - December 31, 2025	$ 0

Stock-Based Awards - Summary of Company's Equity Plans (Details) shares in Millions	12 Months Ended
	Dec. 31, 2025 shares
Employment Inducement Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Year of Adoption	2021
Expiration date, as amended	Feb. 03, 2031
Shares available for future issuance	0.3
Employment Inducement Plan \| Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Maximum number of shares authorized	1.7
2023 Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Year of Adoption	2023
Expiration date, as amended	Jun. 07, 2033
Shares available for future issuance	7.9
2023 Incentive Plan \| Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Maximum number of shares authorized	15.5
2014 Employee Stock Purchase Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Year of Adoption	2014
Expiration date, as amended	Jun. 07, 2033
Shares available for future issuance	6.2
2014 Employee Stock Purchase Plan \| Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Maximum number of shares authorized	7.3

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Stock-Based Awards - Summary of Activity Under Restricted Stock Units (RSUs) from 2014 Plan (Details) - Restricted Stock Units shares in Millions	12 Months Ended
	Dec. 31, 2025 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Number of Shares, Unvested, Beginning Balance \| shares	5.2
Number of shares, granted \| shares	2.9
Number of shares, vested \| shares	(1.5)
Number of shares, cancelled \| shares	(0.7)
Outstanding, Number of Shares, Unvested, Ending Balance \| shares	5.9
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance \| $ / shares	$ 53.22
Weighted-Average Grant Date Fair Value, granted \| $ / shares	41.04
Weighted-Average Grant Date Fair Value, vested \| $ / shares	56.39
Weighted-Average Grant Date Fair Value, cancelled \| $ / shares	49.78
Outstanding, Weighted-Average Grant Date Fair Value, Unvested, Ending Balance \| $ / shares	$ 46.23

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured on Recurring Basis

The following tables set forth the fair value of the Company’s financial assets and liabilities remeasured on a recurring basis based on the three-tier fair value hierarchy (in millions):


	December 31, 2025
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	320	$	—	$	—	$	320
Time deposits		—		10		—		10
Corporate bonds		—		263		—		263
Commercial paper		—		37		—		37
U.S. Government Treasury and agency securities		12		23		—		35
Investment in Solid common stock		3		—		—		3
Deferred compensation assets		—		19		—		19
Total financial assets	$	335	$	352	$	—	$	687

Financial Liabilities:
Deferred compensation liabilities	$	—	$	19	$	—	$	19


	December 31, 2024
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money market funds	$	114	$	—	$	—	$	114
Time deposits		—		10		—		10
Corporate bonds		—		392		—		392
Commercial paper		—		21		—		21
U.S. Government Treasury and agency securities		—		159		—		159
Investment in Solid common stock		2		—		—		2
Deferred compensation assets		—		15		—		15
Total financial assets	$	116	$	597	$	—	$	713

Financial Liabilities:
Deferred compensation liabilities	$	—	$	16	$	—	$	16

Related Party Transaction	12 Months Ended
Related Party Transaction	Dec. 31, 2025
Related Party Transactions [Abstract]
Related Party Transaction	16. Related Party Transaction In July 2022, the Company entered into an agreement with a non-profit foundation in which two members of the Company’s board of directors, including the Company’s Chief Executive Officer, at the time also served as board members of the foundation, whereby an aggregate $1 million contribution is being paid to the foundation over a four-year period, beginning in the third quarter of 2022, to support rare disease education and awareness. A total of $1 million has been recorded as research and development expense for this agreement to date. There are no further obligations under this agreement.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Equity

12 Months Ended

Dec. 31, 2025

Equity [Abstract]

Equity

11.

Equity

At-the-Market Offerings

In February 2024, the Company entered into a Sales Agreement with Cowen and Company, LLC, or Cowen, pursuant to which the Company may offer and sell shares of the Company’s common stock having an aggregate offering proceeds of up to $350 million, from time to time, in at-the-market, or ATM, offerings through Cowen. The Company sold 2.2 million shares under the ATM for net proceeds of $80 million during the year ended December 31, 2025.

In May 2021, the Company entered into an Open Market Sale Agreement with Jefferies LLC, or Jefferies, pursuant to which the Company may offer and sell shares of the Company’s common stock having an aggregate offering proceeds of up to $350 million, from time to time, in ATM offerings through Jefferies. During the year ended December 31, 2023, there were 1.2 million shares sold under the ATM resulting in net proceeds of $53 million.

Underwritten Public Offering

In June 2024, the Company completed an underwritten public offering in which 8.8 million shares of common stock were sold, including the exercise in full by the underwriters of their option to purchase an additional 1.3 million shares, at a public offering price of $39.00 per share. In connection with the offering, the Company sold to certain investors pre-funded warrants, in lieu of common stock, to purchase 1.5 million shares of common stock at a purchase price of $38.999 per pre-funded warrant, which equals the public offering price per share of common stock less the $0.001 exercise price per share of each pre-funded warrant. The total proceeds that the Company received from the offering were $381 million, net of underwriting discounts and commissions.

In October 2023, the Company completed an underwritten public offering in which 9.8 million shares of common stock were sold, including the exercise in full by the underwriters of their option to purchase an additional 1.5 million shares, at a public offering price of $30.00 per share. In connection with the offering, the Company sold to certain investors pre-funded warrants, in lieu of common stock, to purchase 1.7 million shares of common stock at a purchase price of $29.999 per pre-funded warrant, which equals the public offering price per share of common stock less the $0.001 exercise price per share of each pre-funded warrant. The total proceeds that the Company received from the offering were $327 million, net of underwriting discounts and commissions.

The pre-funded warrants were classified as a component of permanent equity in the Company's Consolidated Balance Sheets as they are freestanding financial instruments that are immediately exercisable, do not embody an obligation for the Company to repurchase its own shares and permit the holders to receive a fixed number of shares of common stock upon exercise. All of the shares underlying the pre-funded warrants have been included in the weighted-average number of shares of common stock used to calculate net loss per share, basic and diluted, attributable to common stockholders because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date of the pre-funded warrants. As of December 31, 2025, no pre-funded warrants had been exercised.

The table below summarizes pre-funded warrants activity:


	Pre-funded warrants (millions)
As of December 31, 2023		1.7
Issuance of pre-funded warrants		1.5
As of December 31, 2024		3.2
Changes and adjustments		—
As of December 31, 2025		3.2

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-8A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Subparagraph (b)
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-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 14
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-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (a)
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-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Paragraph 2
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
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-URI https://asc.fasb.org/1943274/2147480237/815-40-50-6

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org/505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

+ Details

Income Taxes - Schedule of Income Taxes Paid (Net of Refunds) (Details)
$ in Millions

12 Months Ended

Dec. 31, 2025

USD ($)

Income Tax Paid, by Individual Jurisdiction [Line Items]

Federal income taxes paid (net of refunds)

$ 0

State income taxes paid (net of refunds)

Total income taxes paid (net of refunds)

Brazil

Income Tax Paid, by Individual Jurisdiction [Line Items]

Foreign income taxes paid (net of refunds)

Mexico

Income Tax Paid, by Individual Jurisdiction [Line Items]

Foreign income taxes paid (net of refunds)

Other

Income Tax Paid, by Individual Jurisdiction [Line Items]

Foreign income taxes paid (net of refunds)

$ 2

^[1]

[1]	There was a nominal amount of foreign taxes paid (net of refunds) to Canada, Switzerland, France, Japan, and the Netherlands.

Equity - Summary of Pre- Funded Warrants Activity (Details) - Pre Funded Warrant - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Stockholders Equity [Line Items]
Beginning Balance	3.2	1.7
Issuance of pre-funded warrants		1.5
Changes and adjustments	$ 0
Ending Balance	3.2	3.2

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Contribution Pension And Other Post Retirement Plan Disclosure [Abstract]
Contribution expenses	$ 10	$ 10	$ 10

Stock-Based Awards - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total estimated fair value of options vested	$ 46	$ 54	$ 60
Total unrecognized compensation cost	$ 232
Weighted-average period to recognize cost	2 years
Stock-based compensation capitalized to inventory	$ 2	3	2
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of shares vested	85	63	55
Aggregate intrinsic value	62	54	33
Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of shares vested	12	3	4
Aggregate intrinsic value	9	2	1
Performance Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total estimated fair value of options vested	$ 14	$ 10	$ 3
Maximum \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	4 years
Minimum \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock based awards vesting period	1 year
2023 Plan and Inducement Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage	25.00%
Stock based awards vesting period	4 years
2023 Plan and Inducement Plan \| Maximum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award expiration period	10 years
2023 Plan and Inducement Plan \| First Anniversary \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage	25.00%
2023 Plan and Inducement Plan \| Shares Vesting Monthly After First Anniversary \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage	2.08%
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of statutory stock awards	85.00%
Common stock shares issued	0.2

Defined Contribution Plan	12 Months Ended
Defined Contribution Plan	Dec. 31, 2025
Defined Contribution Pension And Other Post Retirement Plan Disclosure [Abstract]
Defined Contribution Plan	13. Defined Contribution Plan The Company sponsors a retirement plan in which substantially all of its full-time employees in the U.S. and certain other foreign countries are eligible to participate. Eligible participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. The Company recorded $10 million, $10 million, and $10 million as expense related to the plan for the years ended December 31, 2025, 2024, and 2023, respectively.

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Treasury Stock	Deferred Compensation Obligation
Beginning balance at Dec. 31, 2022	$ 352		$ 3,140	$ (7)	$ (2,781)
Beginning balance, shares at Dec. 31, 2022		70,200,000
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs	326		326
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs,shares		9,800,000
Issuance of common stock in connection with at-the-market offering, net of issuance costs	$ 53		53
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares	1,200,000	1,200,000
Stock-based compensation	$ 135		135
Issuance of common stock under equity plan awards, net of tax	8		8
Issuance of common stock under equity plan awards, net of tax, shares		1,100,000
Other comprehensive income (loss)	8			8
Net loss	(607)				(607)
Ending balance at Dec. 31, 2023	275		3,662	1	(3,388)
Ending balance, shares at Dec. 31, 2023		82,300,000
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs	381		381
Issuance of common stock and pre-funded warrants in connection with underwritten public offering, net of issuance costs,shares		8,800,000
Stock-based compensation	159		159
Issuance of common stock under equity plan awards, net of tax	11		11
Issuance of common stock under equity plan awards, net of tax, shares		1,400,000
Deferred compensation						$ (4)	$ 4
Other comprehensive income (loss)	(2)			(2)
Net loss	(569)				(569)
Ending balance at Dec. 31, 2024	$ 255		4,213	(1)	(3,957)	(4)	4
Ending balance, shares at Dec. 31, 2024	92,500,000	92,500,000
Issuance of common stock in connection with at-the-market offering, net of issuance costs	$ 80		80
Issuance of common stock in connection with at-the-market offering, net of issuance costs, shares		2,200,000
Stock-based compensation	152		152
Issuance of common stock under equity plan awards, net of tax	6		6
Issuance of common stock under equity plan awards, net of tax, shares		1,900,000
Deferred compensation						(4)	4
Other comprehensive income (loss)	2			2
Net loss	(575)				(575)
Ending balance at Dec. 31, 2025	$ (80)		$ 4,451	$ 1	$ (4,532)	$ (8)	$ 8
Ending balance, shares at Dec. 31, 2025	96,600,000	96,600,000

License and Research Agreements - Mereo - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development		$ 750	$ 698	$ 648
Regulatory milestone payments achieved		9	30
License and Collaboration Agreement \| Mereo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development				$ 9
Offset to research and development expense		(5)	(1)
License agreement accounts receivable		1	$ 1
Payments made under agreement	$ 50
License and Collaboration Agreement \| Maximum \| Mereo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments		$ 245

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	250,000,000	250,000,000
Common Stock Shares Issued Not Disclosed	true	true
Common stock, shares outstanding	96,600,000	92,500,000
Treasury stock , shares	200,000	100,000
Cash and cash equivalents	$ 421	$ 174

License and Research Agreements

12 Months Ended

Dec. 31, 2025

Research Grant Agreement [Abstract]

License and Research Agreements

Kyowa Kirin Co., Ltd.

In August 2013, the Company entered into a collaboration and license agreement with Kyowa Kirin Co., Ltd., or KKC. Under the terms of this collaboration and license agreement, as amended, the Company and KKC collaborate on the development and commercialization of Crysvita in the field of orphan diseases in the U.S. and Canada, or the Profit-Share Territory, and in the European Union, UK, and Switzerland, or the European Territory, and the Company has the right to develop and commercialize such products in the field of orphan diseases in Mexico and Central and South America, or Latin America.

The collaboration and license agreements are within the scope of ASC 808, which provides guidance on the presentation and disclosure of collaborative arrangements.

Product Sales Revenue for Latin America and Türkiye

The Company is responsible for commercializing Crysvita in Latin America and Türkiye. The Company is considered the principal in these territories as the Company controls the product before it is transferred to the customer. Accordingly, the Company records revenue on a gross basis for the sale of Crysvita once the product is delivered and the risk and title of the product is transferred to the distributor. In Türkiye, KKC has the option to assume responsibility for commercialization efforts.

Transfer Price and Royalties on Product Sales Revenue

Under the collaboration agreement, KKC manufactures and supplies Crysvita, which is purchased by the Company for sales in Latin America and Türkiye. KKC charges the Company a transfer price of 30% of net sales for supply of product to Latin America. The Company also pays to KKC a low single-digit royalty on net sales in Latin America.

Collaboration and Royalty Revenue for Sales in the Profit-Share Territory

The Company and KKC shared commercial responsibilities and profits in the Profit-Share Territory until April 2023. Under the collaboration agreement, KKC manufactured and supplied Crysvita for commercial use in the Profit-Share Territory and charged the Company a transfer price of 30% of net sales in 2023. The remaining profit or loss after supply costs from commercializing products in the Profit-Share Territory was shared between the Company and KKC on a 50/50 basis until April 2023. In April 2023, commercialization responsibilities for Crysvita in the Profit-Share Territory transitioned to KKC. Thereafter, the Company is entitled to receive a tiered double-digit revenue share from the mid-20% range up to a maximum rate of 30%.

During the prior profit-share period, as KKC was the principal in the sale transaction with the customer, the Company recognized a pro-rata share of collaboration revenue, net of transfer pricing, in the period the sale occurred. The Company concluded that its portion of KKC’s sales in the Profit-Share Territory prior to April 2023 was analogous to a royalty and therefore recorded its share as collaboration revenue, similar to a royalty. Starting in April 2023, the Company began to record as royalty revenue in the period the underlying sales occurred.

In July 2022, the Company sold to OMERS its right to receive 30% of the future royalty payments, beginning in April 2023, that are due to the Company based on net sales of Crysvita in the U.S. and Canada, subject to a cap. In November 2025, the Company sold to OMERS its right to an additional 25% of the future royalty payments, beginning in January 2028, that are due to the Company based on net sales of Crysvita in the U.S. and Canada, subject to a cap. These agreements are further described in “Note 10. Liabilities for Sales of Future Royalties.”

Royalty Revenue for Sales in the European Territory

KKC has commercial responsibility for Crysvita in the European Territory. Under the collaboration agreement, the Company is entitled to receive royalties of up to 10% of net sales in the European Territory, which are recorded as royalty revenue as the underlying sales occur. In December 2019, the Company sold its right to receive these royalty payments to Royalty Pharma, effective January 1, 2020, as further described in “Note 10. Liabilities for Sales of Future Royalties.”

Total Crysvita revenue was as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Product sales	$	177	$	135	$	75
Revenue in Profit-Share Territory:
Royalty revenue		192		174		113
Non-cash royalty revenue		83		75		49
Collaboration revenue		—		—		70
Total revenue in Profit-Share Territory		275		249		232
Non-cash royalty revenue in European Territory		29		26		21
Total Crysvita revenue	$	481	$	410	$	328

Collaboration Cost Sharing and Payments

Under the collaboration agreement, KKC and the Company share certain development and commercialization costs, and as a result, the Company was reimbursed for these costs and operating expenses were reduced. KKC also receives a transfer price and royalty on net product sales revenue which is recorded in cost of sales. These amounts were recognized in the Company’s Consolidated Statements of Operations in connection with the collaboration agreement with KKC as follows (in millions):


	Year Ended December 31,
	2025			2024			2023
Research and development	$	(5	)	$	(4	)	$	(7	)
Selling, general and administrative	$	—		$	(4	)	$	(17	)
Cost of sales	$	61		$	46		$	18

Collaboration Receivable and Payable

The Company had accounts receivable from KKC in the amount of $98 million and $85 million from royalties, other receivables of $1 million and $2 million recorded in other current assets, and accrued liabilities of $12 million and $7 million from amounts owed for transfer price and royalties as well as commercial and development activity reimbursements, as of December 31, 2025 and 2024, respectively.

Regeneron

In January 2022, the Company entered into a collaboration with Regeneron to commercialize Evkeeza for HoFH outside of the U.S. Pursuant to the terms of the agreement, the Company received the rights to develop, commercialize and distribute the product for HoFH in countries outside of the U.S. The Company paid Regeneron a $30 million upfront payment. As of December 31, 2025, the Company has recognized an aggregate of $33 million for regulatory and sales milestones under the agreement. As these payments are for the Company’s use of intellectual property for Evkeeza for HoFH, they were recorded as intangible assets. See "Note 5. Intangible Assets, net" for additional details. The Company is required to pay up to an aggregate of $31 million in the future contingent upon the achievement of certain regulatory and sales milestones. The Company may share in certain costs for global trials led by Regeneron. Additionally, the Company pays Regeneron a product purchase price and royalties on certain revenues.

The collaboration agreement is within the scope of ASC 808 which provides guidance on the presentation and disclosure of collaborative arrangements. As the Company is the principal in sales transactions with the customer, the Company recognizes product sales and cost of sales in the period the related sales occur and the related revenue recognition criteria are met. Under the collaboration agreement, Regeneron supplies the product and charges the Company a product purchase price from the low 20% range up to 40% on net sales, which is recognized as cost of sales in the Company’s Consolidated Statement of Operations.

Under the collaboration agreement, Regeneron and the Company share certain development and commercialization costs. Regeneron also receives a product purchase price and royalty on net product sales revenue which is recorded in cost of sales. These amounts were recognized in the Company’s Consolidated Statements of Operations in connection with the collaboration agreement with Regeneron as follows (in millions):


	Year Ended December 31,
	2025		2024			2023
Research and development	$	1	$	(3	)	$	8
Cost of sales	$	16	$	8		$	1

The Company had collaboration payables for this arrangement included in accrued liabilities on the Consolidated Balance Sheets of $9 million and $18 million as of December 31, 2025 and 2024, respectively.

Saint Louis University

In November 2010, the Company entered into a license agreement with Saint Louis University, or SLU. Under the terms of this license agreement, SLU granted the Company an exclusive worldwide license to make, have made, use, import, offer for sale, and sell therapeutics related to SLU’s beta-glucuronidase product for use in the treatment of human diseases.

Under the license agreement, the Company is obligated to pay to SLU a low single-digit royalty on net sales of the licensed products in Europe and Japan, subject to certain potential deductions. The Company's obligation to pay royalties to SLU in these territories continues until the expiration of any orphan drug exclusivity.

Abeona

In May 2022, the Company announced an exclusive License Agreement for the AAV gene therapy for UX111 with Abeona for the treatment of MPS IIIA. Under the terms of the agreement, the Company assumed responsibility for the UX111 program and in return, the Company is obligated to pay tiered royalties of up to 10% on net sales and commercial milestone payments of up to $30.0 million contingent upon regulatory approval of the product. Additionally, the Company entered into an Assignment and Assumption Agreement with Abeona to transfer and assign to the Company the exclusive license agreement between Nationwide Children’s Hospital, or NCH, and Abeona for certain rights related to UX111. Under this agreement, the Company is obligated to pay up to $1 million contingent upon achievement of development and regulatory milestones as well as royalties in the low single-digits of net sales.

Mereo

In December 2020, the Company entered into a License and Collaboration Agreement with Mereo to collaborate on the development of setrusumab. Under the terms of the agreement, as amended, the Company will lead future global development of setrusumab in both pediatric and adult patients with OI. The Company was granted an exclusive license to develop and commercialize setrusumab in the U.S., Türkiye, and the rest of the world, or the Ultragenyx Territory, excluding the EEA, UK, and Switzerland, or the Mereo Territory, where Mereo retains commercial rights. Each party will be responsible for post-marketing

commitments in their respective territories and Ultragenyx will be responsible for commercial supply in both the Ultragenyx Territory and Mereo Territory.

Upon the closing of the transactions under the License and Collaboration Agreement with Mereo in January 2021, the Company made a payment of $50 million to Mereo. As of December 31, 2025, the Company has made payments totaling $9 million for regulatory milestones achieved. The Company is obligated to pay Mereo up to $245 million in future milestone payments, contingent upon the achievement of certain regulatory and commercial milestones. The Company pays for all global development costs and will pay a tiered double-digit percentage royalties to Mereo on net sales in the Ultragenyx Territory. Mereo will pay the Company a fixed double-digit percentage royalty on net sales in the Mereo Territory. If the Company receives and resells an FDA priority review voucher, or PRV, in connection with a new drug application approval, Mereo is entitled to receive a portion of proceeds from the sale of the PRV or a cash payment from the Company, in the event the Company chooses to retain the PRV.

In December 2024, the Company entered into a manufacturing and supply agreement with Mereo where it is responsible for the supply of setrusumab to Mereo in the Mereo Territory. Mereo is responsible for reimbursing us for a portion of the manufacturing process development costs as well as future commercial supply costs.

Although Mereo is a VIE, the Company is not the primary beneficiary as it does not have the power to direct the activities that would most significantly impact the economic performance of Mereo. Prior to the achievement of certain development milestones, all consideration paid to Mereo represents rights to potential future benefits associated with Mereo’s in-process research and development activities, which have not reached technological feasibility and have no alternative future use.

For the years ended December 31, 2025 and 2024, the Company recorded offsets to research and development expense of $5 million and $1 million, respectively. For the year ended December 31, 2023, the Company recorded development costs of $9 million for the achievement of a clinical milestone recorded in research and development expense.

As of December 31, 2025 and 2024, the Company had receivables from Mereo in the amount of $1 million and $1 million, respectively, recorded in other current assets for development activity reimbursements.

GeneTx Biotherapeutics LLC

In August 2019, the Company entered into a Program Agreement and a Unitholder Option Agreement with GeneTx Biotherapeutics LLC, or GeneTx, as subsequently amended, or the Option Agreement, to collaborate on the development of GeneTx’s GTX-102, an ASO for the treatment of Angelman syndrome. In July 2022, the Company exercised its option to acquire GeneTx, pursuant to the terms of the Option Agreement. During the year ended December 31, 2024, the Company achieved a $30 million regulatory milestone upon the initiation of the Phase 3 Aspire clinical study for GTX-102. The Company is obligated to pay up to $85 million in additional regulatory approval milestones for the achievement of U.S. and EU product approvals, and up to $75 million in commercial milestone payments based on annual worldwide net product sales, contingent upon the achievement of the milestones. The Company will also pay tiered mid- to high single-digit percentage royalties based on licensed product annual net sales. If the Company receives and resells an FDA priority review voucher, or PRV, in connection with a new drug application approval, GeneTx unitholders are entitled to receive a portion of proceeds from the sale or a cash payment from the Company if the Company chooses to retain the PRV.

As part of the Company's acquisition of GeneTx, the Company assumed a License Agreement with Texas A&M University, or TAMU. The Company recognized an aggregate of $1 million for clinical milestones under the TAMU agreement, and has future obligations up to $23 million for various milestones and a nominal annual license fee that may increase up to a maximum of $2 million. The Company will also pay mid-single-digit percentage royalties based on licensed product annual net sales. As of December 31, 2025 and 2024, the Company had nil and $1 million, respectively, in collaboration payables under this arrangement.

Prior to the achievement of certain development and regulatory milestones, amounts paid towards the milestones are classified as in-process research and development expense, as the acquired in-process research and development intangible asset has not yet reached technological feasibility and has no alternative future use.

University of Pennsylvania

The Company has a research, collaboration, and license agreement with University of Pennsylvania School of Medicine, or Penn, which provides the terms for the Company and Penn to collaborate with respect to the pre-clinical development of gene therapy products for the treatment of certain indications. Under the agreement, Penn granted the Company an exclusive, worldwide license to certain patent rights arising out of the research program, subject to certain retained rights, and a non-exclusive, worldwide license to certain Penn intellectual property, in each case to research, develop, make, have made, use, sell, offer for sale, commercialize and import licensed products in each indication for the term of the agreement. The Company will fund the cost of the research program in accordance with a mutually agreed-upon research budget and will be responsible for clinical development,

manufacturing and commercialization of each indication. The Company is obligated to make milestone payments of up to $5 million for each indication, if certain development milestones are achieved. The Company is also obligated to make milestone payments of up to $25 million per approved product, if certain commercial milestones are achieved, as well as low to mid- single-digit royalties on net sales of each licensed product.

REGENXBIO, Inc.

The Company has a license agreement with REGENXBIO, Inc., or REGENX, for an exclusive, sublicensable, worldwide commercial license under certain intellectual property for preclinical and clinical research and development, and commercialization of drug therapies using REGENX's licensed patents for the treatment of OTC deficiency and GSD1a. The Company will pay an annual fee and certain milestone fees per disease indication, low to mid- single-digit royalty percentages on net sales of licensed products, and milestone and sublicense fees owed by REGENX to its licensors, which are contingent upon the attainment of certain development activities as outlined in the agreement. This license agreement was terminated for certain indications in November 2025.

The Company also had an option and license agreement with REGENX under which the Company had an exclusive, sublicensable, worldwide license to make, have made, use, import, sell, and offer for sale licensed products to treat Wilson disease and CDKL5 deficiency. This option and license agreement was terminated in November 2025.

Stock-Based Awards - Summary of Stock-Based Compensation Recognized (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 153	$ 158	$ 135
Cost of sales
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2	1	1
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	84	87	75
Selling, general and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 67	$ 70	$ 59

Net Loss per Share - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Numerator:
Net loss	$ (575)	$ (569)	$ (607)
Denominator:
Weighted-average shares used to computing net loss per share, basic	98.6	90.5	73.5
Weighted-average shares used to computing net loss per share, diluted	98.6	90.5	73.5
Net loss per share, basic	$ (5.83)	$ (6.29)	$ (8.25)
Net loss per share, diluted	$ (5.83)	$ (6.29)	$ (8.25)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Balance Sheet Components

12 Months Ended

Dec. 31, 2025

Investments, Debt and Equity Securities [Abstract]

Balance Sheet Components

Cash Equivalents and Marketable Securities

The fair values of cash equivalents and marketable securities classified as available-for-sale securities consist of the following (in millions):


	December 31, 2025
	Amortized		Gross Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Money market funds	$	320	$	—	$	—	$	320
Time deposits		10		—		—		10
Corporate bonds		263		—		—		263
Commercial paper		37		—		—		37
U.S. Government Treasury and agency securities		35		—		—		35
Total	$	665	$	—	$	—	$	665


	December 31, 2024
	Amortized		Gross Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Money market funds	$	114	$	—	$	—	$	114
Time deposits		10		—		—		10
Corporate bonds		391		1				392
Commercial paper		21		—		—		21
U.S. Government Treasury and agency securities		159		—		—		159
Total	$	695	$	1	$	—	$	696

At December 31, 2025, the remaining contractual maturities of available-for-sale securities were less than two years. The cost of securities sold is based on the specific-identification method. There have been no significant realized gains or losses on available-for-sale securities for the periods presented. All marketable securities with unrealized losses at December 31, 2025 have been in a loss position for less than 12 months or the loss is not material and is temporary in nature.

Inventory

Inventory consists of the following (in millions):


	December 31,
	2025		2024
Work-in-process	$	27	$	22
Finished goods		25		23
Total inventory	$	52	$	45

Property, Plant, and Equipment, net

Property, plant, and equipment, net consists of the following (in millions):


		December 31,
	Useful life (years)	2025			2024
Building	20-30	$	182		$	182
Leasehold improvements	Shorter of lease term or estimated useful life		55			58
Research and development equipment	5		65			60
Furniture and office equipment	5		7			6
Computer equipment and software	3-5		16			16
Manufacturing equipment	5-15		37			37
Land	Not applicable		17			17
Other	Varies by asset		1			2
Property, plant, and equipment, gross			380			378
Less: accumulated depreciation			(136	)		(112	)
Property, plant, and equipment, net		$	244		$	266

Depreciation expense for the years ended December 31, 2025, 2024, and 2023 was $27 million, $30 million and $22 million, respectively. Amortization of leasehold improvements and software is included in depreciation expense.

Accrued Liabilities

Accrued liabilities consist of the following (in millions):


	December 31,
	2025		2024
Research and clinical study expenses	$	23	$	24
Payroll and related expenses		89		94
Revenue related reserves		57		33
Manufacturing and related expenses		67		25
Commercial and development milestones		5		45
Other		24		20
Total accrued liabilities	$	265	$	241

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Current assets:
Cash and cash equivalents	$ 421	$ 174
Marketable securities	259	436
Accounts receivable, net	158	122
Inventory	52	45
Prepaid expenses and other assets	61	40
Total current assets	951	817
Property, plant, and equipment, net	244	266
Marketable securities	57	135
Intangible assets, net	176	178
Goodwill	44	44
Other assets	60	63
Total assets	1,532	1,503
Current liabilities:
Accounts payable	31	39
Accrued liabilities	265	241
Lease liabilities	12	10
Liabilities for sales of future royalties	69	50
Other liabilities	7	4
Total current liabilities	384	344
Lease liabilities	24	30
Deferred tax liabilities	30	30
Liabilities for sales of future royalties	1,147	820
Other liabilities	20	17
Total liabilities	1,605	1,241
Commitments and contingencies (Note 15)
Noncontrolling interest	7	7
Stockholders' equity (deficit):
Preferred stock, par value of $0.001 per share-25.0 shares authorized; nil outstanding in 2025 and in 2024	0	0
Common stock, par value of $0.001 per share-250.0 shares authorized; outstanding-96.6 in 2025 and 92.5 in 2024	0	0
Treasury stock, at cost, 0.2 shares in 2025 and 0.1 shares in 2024	(8)	(4)
Deferred compensation obligation	8	4
Additional paid-in capital	4,451	4,213
Accumulated other comprehensive income (loss)	1	(1)
Accumulated deficit	(4,532)	(3,957)
Total stockholders' equity (deficit)	(80)	255
Total liabilities, noncontrolling interest and stockholders' equity (deficit)	$ 1,532	$ 1,503

License and Research Agreements - University of Pennsylvania - Additional Information (Details) - University of Pennsylvania School of Medicine (Penn) $ in Millions	Dec. 31, 2025 USD ($)
Research Collaboration and License Agreement Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 5
Research Collaboration and License Agreement Commercial Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	$ 25

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Short-Term Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Deferred compensation liabilities	$ 1	$ 1
Long-Term Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Deferred compensation liabilities	$ 18	$ 15

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Intangible Assets, Net - Additional Information (Details) 1 - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
IPR&D Assets
Indefinite-Lived Intangible Assets [Line Items]
Business combination recognized intangible assets	$ 129	$ 129

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Leases - Schedule of Maturities of Lease Liabilities and the Reconciliation of Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Operating
2026	$ 15
2027	10
2028	8
2029	7
2030	2
Thereafter	1
Total future lease payments	43
Less: Amount representing interest	(7)
Present value of future lease payments	36
Less: Lease liabilities, current	$ (12)	$ (10)
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Less: Lease liabilities, current
Lease liabilities, non-current	$ 24	$ 30
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Lease liabilities, non-current

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2025 Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable segments	1

Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization and Basis of Presentation

Ultragenyx Pharmaceutical Inc., or the Company, is a biopharmaceutical company incorporated in Delaware.

The Company is focused on the identification, acquisition, development, and commercialization of novel products for the treatment of serious rare and ultra-rare genetic diseases. The Company operates as one reportable segment and has four commercially approved products.

Crysvita® (burosumab) is approved in the United States, or U.S., the European Union, or EU, and certain other regions for the treatment of X-linked hypophosphatemia, or XLH, in adult and pediatric patients one year of age and older. Crysvita is also approved in the U.S. and certain other regions for the treatment of fibroblast growth factor 23, or FGF23-related hypophosphatemia in tumor-induced osteomalacia, or TIO, associated with phosphaturic mesenchymal tumors that cannot be curatively resected or localized in adults and pediatric patients 2 years of age and older.

Mepsevii® (vestronidase alfa) is approved in the U.S., the EU and certain other regions, as the first medicine for the treatment of children and adults with mucopolysaccharidosis VII, or MPS VII, also known as Sly syndrome.

Dojolvi® (triheptanoin) is approved in the U.S. and certain other regions for the treatment of pediatric and adult patients severely affected by long-chain fatty acid oxidation disorders, or LC-FAOD.

Evkeeza® (evinacumab) is approved in the U.S. and the European Economic Area, or EEA, and Japan for the treatment of homozygous familial hypercholesterolemia, or HoFH. The Company has exclusive rights to commercialize Evkeeza® (evinacumab) outside of the U.S.

In addition to the approved products, the Company has the following ongoing clinical development programs:

•

UX111 (formerly ABO-102) is an AAV9 gene therapy product candidate for the treatment of patients with Sanfilippo syndrome type A, or MPS IIIA, a rare lysosomal storage disease;

•

DTX401 is an adeno-associated virus 8, or AAV8, gene therapy product candidate for the treatment of patients with glycogen storage disease type Ia, or GSDIa;

•

GTX-102 is an antisense oligonucleotide, or ASO for the treatment of Angelman syndrome, a debilitating and rare neurogenetic disorder caused by loss-of-function of the maternally inherited allele of the UBE3A gene;

•

DTX301 is an AAV8 gene therapy product candidate in development for the treatment of patients with ornithine transcarbamylase, or OTC deficiency, the most common urea cycle disorder;

•

UX701 is an adeno-associated virus 9, or AAV9, gene therapy designed to deliver stable expression of a truncated version of the ATP7B copper transporter following a single intravenous infusion to improve copper distribution and excretion from the body and reverse pathological findings of Wilson liver disease; and

•

UX143 which is subject to the Company’s collaboration agreement with Mereo BioPharma 3, or Mereo, is a fully human monoclonal antibody that inhibits sclerostin, a protein that acts on a key bone-signaling pathway and inhibits the activity of bone-forming cells for the treatment of patients with Osteogenesis Imperfecta, or OI.

The Company has sustained operating losses and expects such annual losses to continue in the near term. The Company’s ultimate success depends on the outcome of its research and development and commercialization activities. Through December 31, 2025, the Company has relied primarily on the sale of equity securities, revenues from commercial products, the sale of certain future royalties, and strategic collaboration arrangements to finance its operations. The Company may need to raise additional capital to fully implement its business plans through the issuance of equity, borrowings, or strategic alliances with partner companies. However, if such financing is not available at adequate levels, the Company would need to reevaluate its operating plans.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2025
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Leases - Summary of Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Lease, Cost [Abstract]
Operating lease expense	$ 12	$ 12	$ 13
Variable lease expense	5	6	5
Total	$ 17	$ 18	$ 18

Liabilities for Sales of Future Royalties

12 Months Ended

Dec. 31, 2025

Deferred Revenue Disclosure [Abstract]

Liabilities for Sales of Future Royalties

10.

Liabilities for Sales of Future Royalties

In December 2019, the Company entered into a Royalty Purchase Agreement with RPI. Pursuant to the agreement, RPI paid $320 million to the Company in consideration for the right to receive royalty payments effective January 1, 2020, arising from the net sales of Crysvita in the EU, the U.K., and Switzerland under the terms of the Company’s Collaboration and License Agreement with KKC dated August 29, 2013, as amended, or the KKC Collaboration Agreement. The agreement with RPI will automatically terminate, and the payment of royalties to RPI will cease, in the event aggregate royalty payments received by RPI are equal to or greater than $608.0 million prior to December 31, 2030, or in the event aggregate royalty payments received by RPI are less than $608 million prior to December 31, 2030, or when aggregate royalty payments received by RPI are equal to $800 million.

In July 2022, the Company entered into a Royalty Purchase Agreement with OMERS, or the 2022 OMERS Agreement. Pursuant to the agreement, OMERS paid $500 million to the Company in consideration for the right to receive 30% of the future royalty payments due to the Company from KKC based on net sales of Crysvita in the U.S. and Canada under the terms of the KKC Collaboration Agreement. The calculation of royalty payments to OMERS is based on net sales of Crysvita beginning in April 2023 and will expire upon the earlier of the date on which aggregate payments received by OMERS equals $725 million or on the date the final royalty payment is made to the Company under the KKC Collaboration Agreement.

In November 2025, the Company entered into a second Royalty Purchase Agreement with OMERS, or the 2025 OMERS Agreement. Pursuant to the agreement, OMERS paid $400 million to the Company in exchange for the right to receive an additional 25% of future royalty payments, starting on January 1, 2028, on net sales of Crysvita in the U.S. and Canada. OMERS will also continue to receive 30% of Crysvita net sales in the U.S. and Canada following the achievement of $725 million in aggregate payments under the 2022 OMERS Agreement. The 2025 OMERS Agreement will expire upon the earlier of the date on which aggregate payments received by OMERS under this transaction equal $620 million or on the date the final royalty payment is made to the Company under the KKC Collaboration Agreement. Under the agreement, OMERS granted the Company an option to repurchase the entire purchased interest, that expires in November 2027, for 1.35 times the purchase price, or $540 million.

Proceeds from these transactions were recorded as liabilities for sales of future royalties on the Consolidated Balance Sheets. Upon inception of the respective arrangements, the Company recorded liabilities of $320 million, $500 million, and $400 million, net of transaction costs of $6 million, $9 million, and $8 million, for the RPI Agreement, the 2022 OMERS Agreement, and the 2025 OMERS Agreement, respectively. The Company records the royalty revenue arising from the net sales of Crysvita in the applicable territories as royalty revenue in the Consolidated Statements of Operations over the term of the arrangements. Royalties earned under the RPI Agreement, the 2022 OMERS Agreement, and the 2025 OMERS Agreement from inception to December 31, 2025 have been $128 million, $206 million, and nil, respectively. The Company’s effective annual interest rates were 5.5%, 7.3%, and 9.2% for the RPI Agreement, the 2022 OMERS Agreement, and the 2025 OMERS Agreement, respectively, as of December 31, 2025.

There are a number of factors that could materially affect the amount and timing of royalty payments from KKC in the applicable territories, most of which are not within the Company’s control. Such factors include, but are not limited to, the success of KKC’s sales and promotion of Crysvita, changing standards of care, macroeconomic and inflationary pressures, the introduction of competing products, pricing for reimbursement in various territories, manufacturing or other delays, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of Crysvita, significant changes in foreign exchange rates as the royalty payments are made in U.S. dollars, or USD, while significant portions of the underlying sales of Crysvita are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from sales of Crysvita, all of which would result in a reduction of royalty revenue and the non-cash interest expense over the life of the arrangement. Conversely, if sales of Crysvita in the relevant territories are more than expected, the royalty revenue and the non-cash interest expense recorded by the Company would be greater over the term of the arrangements.

The following table shows the activity within the liability account (in millions):



	Liabilities for Sales of Future Royalties
	RPI			OMERS 2022			OMERS 2025		Total
December 31, 2023	$	377		$	515		$	—	$	892
Royalty revenue		(26	)		(59	)		—		(85	)
Non-cash interest expense		24			39			—		63
December 31, 2024		375			495			—		870
Net proceeds from sale of future royalties		—			—			392		392
Royalty revenue		(29	)		(79	)		—		(108	)
Non-cash interest expense		20			36			6		62
December 31, 2025	$	366		$	452		$	398	$	1,216

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2025

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss per Share

The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2025, 2024, and 2023 (in millions, except per share data):


	Year Ended December 31,
	2025			2024			2023
Numerator:
Net loss	$	(575	)	$	(569	)	$	(607	)
Denominator:
Weighted-average shares used to compute net loss per share, basic and diluted		98.6			90.5			73.5
Net loss per share, basic and diluted	$	(5.83	)	$	(6.29	)	$	(8.25	)

Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share


	Year Ended December 31,
	2025		2024		2023
Options to purchase common stock, restricted stock units, and performance stock units		16.8		16.3		14.2

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 421	$ 174	$ 214
Restricted cash included in other current assets	13	7	2
Restricted cash included in other non-current assets	2	3	3
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 436	$ 184	$ 219	$ 138

License and Research Agreements - REGENXBIO, Inc. - Additional Information (Details)	12 Months Ended
	Dec. 31, 2025
Option and License Agreement \| REGENXBIO, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Option and license agreement description	The Company also had an option and license agreement with REGENX under which the Company had an exclusive, sublicensable, worldwide license to make, have made, use, import, sell, and offer for sale licensed products to treat Wilson disease and CDKL5 deficiency

Income Taxes - Components of Company's Loss Before Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Domestic	$ 565	$ 563	$ 609
Foreign	6	4	0
Total loss before income taxes	$ 571	$ 567	$ 609

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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+ Details

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Operating activities:
Net loss	$ (575)	$ (569)	$ (607)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	153	158	135
Amortization of discount on marketable securities, net	(4)	(13)	(13)
Depreciation and amortization	35	36	26
Non-cash royalty revenue	(112)	(101)	(69)
Non-cash interest expense on liabilities for sales of future royalties	62	63	66
Other	(2)	(2)	3
Changes in operating assets and liabilities:
Accounts receivable	(31)	(34)	(23)
Inventory	(6)	(11)	(7)
Prepaid expenses and other assets	(10)	12	15
Accounts payable, accrued, and other liabilities	24	47	(1)
Net cash used in operating activities	(466)	(414)	(475)
Investing activities:
Purchase of property, plant, and equipment	(6)	(7)	(44)
Purchase of marketable securities	(186)	(409)	(526)
Proceeds from sale of marketable securities	0	3	51
Proceeds from maturities of marketable securities	444	410	696
Payments for intangible asset	(15)	(13)	(3)
Other	(1)	(2)	(6)
Net cash provided by (used in) investing activities	236	(18)	168
Financing activities:
Proceeds from the sale of future royalties, net	392	0	0
Proceeds from the issuance of common stock and pre-funded warrants in connection with underwritten public offerings, net	0	381	326
Proceeds from the issuance of common stock in connection with at-the-market offering, net	80	0	53
Proceeds from the issuance of common stock under equity plans, net	6	11	8
Proceeds from issuance of equity from noncontrolling interest	0	7	0
Other	0	0	1
Net cash provided by financing activities	478	399	388
Effect of exchange rate changes on cash	4	(2)	0
Net increase (decrease) in cash, cash equivalents, and restricted cash	252	(35)	81
Cash, cash equivalents, and restricted cash at beginning of year	184	219	138
Cash, cash equivalents, and restricted cash at end of year	436	184	219
Supplemental disclosures of non-cash information:
Acquired lease liabilities arising from obtaining right-of-use assets and property, plant, and equipment	6	10	22
Non-cash interest expense on liabilities for sales of future royalties capitalized during the year into ending property, plant and equipment	0	0	9
Costs of intangible assets included in accounts payable, accrued and other liabilities	$ 5	$ 15	$ 10

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 97	$ 80	$ 67
Additions based on tax positions related to current year	15	15	12
Additions for tax positions of prior years	0	2	1
Reductions for tax positions of prior years	(1)	0	0
Balance at end of year	$ 111	$ 97	$ 80

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Basis of Consolidation

Segment Reporting

Use of Estimates

Cash, Cash Equivalents, and Restricted Cash


	December 31,
	2025		2024		2023
Cash and cash equivalents	$	421	$	174	$	214
Restricted cash included in other current assets		13		7		2
Restricted cash included in other non-current assets		2		3		3
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$	436	$	184	$	219

Marketable Securities

Equity Investments

Concentration of Credit Risk, Credit Losses, and Other Risks and Uncertainties

Inventory

Property, Plant, and Equipment

Intangible Assets

Goodwill

Impairment of Long-Lived Assets

Accruals of Research and Development Costs

Liabilities for Sales of Future Royalties

Revenue Recognition

Product Sales

Collaboration, License, and Royalty Revenue

Deferred Compensation Plan

Leases

Comprehensive Loss

Research and Development

Stock-Based Compensation

Income Taxes

Foreign Currency

Net Loss per Share

Recent Accounting Pronouncements

Revenue - Summary of Disaggregation of Total Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation Of Revenue [Line Items]
Total revenues	$ 673	$ 560	$ 434
North America
Disaggregation Of Revenue [Line Items]
Total revenues	377	340	307
Latin America
Disaggregation Of Revenue [Line Items]
Total revenues	170	131	77
Europe, Middle East, and Africa
Disaggregation Of Revenue [Line Items]
Total revenues	108	80	48
Asia-Pacific
Disaggregation Of Revenue [Line Items]
Total revenues	$ 18	$ 9	$ 2

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Related Party Transaction - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended			42 Months Ended
	Jul. 31, 2022	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2025
Related Party Transaction [Line Items]
Total Contract Value	$ 1
Contribution period	4 years
Research and development		$ 750	$ 698	$ 648
Non Profit Foundation [Member]
Related Party Transaction [Line Items]
Research and development					$ 1

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Intangible Assets, Net - Summary of Company's Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	$ 197	$ 191
Intangible assets - Accumulated Amortization	(21)	(13)
Intangible assets - Net Carrying Amount	176	178
Indefinite-lived Intangible Assets
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	129	129
Intangible assets - Net Carrying Amount	129	129
Finite lived intangible assets
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Intangible assets - Gross carrying amount	$ 68	$ 62
Intangible assets - Weighted Average Life	9 years	9 years
Intangible assets - Accumulated Amortization	$ (21)	$ (13)
Intangible assets - Net Carrying Amount	$ 47	$ 49

Leases

12 Months Ended

Dec. 31, 2025

Lessee Disclosure [Abstract]

Leases

The Company leases office space and research, testing and manufacturing laboratory space in various facilities in Novato and Brisbane, California, in Somerville and Woburn, Massachusetts, and in certain foreign countries, under operating agreements expiring at various dates through 2031. Certain lease agreements include options for the Company to extend the lease for multiple renewal periods and provide for annual minimum increases in rent, usually based on a consumer price index or annual minimum increases. None of these optional periods have been considered in the determination of the right-of-use lease asset or the lease liability for the leases as the Company did not consider it reasonably certain that it would exercise any such options. The Company recognizes lease expense on a straight-line basis over the non-cancelable term of its operating leases. The variable lease expense primarily consists of common area maintenance and other operating costs.

The components of lease expense were as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Operating lease expense	$	12	$	12	$	13
Variable lease expense		5		6		5
Total	$	17	$	18	$	18

Cash paid for amounts included in the measurement of operating lease liabilities for the years ended December 31, 2025, 2024, and 2023 was $14 million, $16 million, and $13 million, respectively, and was included in net cash used in operating activities in the Consolidated Statements of Cash Flows.

Right-of-use lease assets were $23 million and $26 million as of December 31, 2025 and 2024, respectively, and were included in other non-current assets on the Consolidated Balance Sheets.

The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2025 (in millions):


Year Ending December 31,	Operating
2026	$	15
2027		10
2028		8
2029		7
2030		2
Thereafter		1
Total future lease payments		43
Less: Amount representing interest		(7	)
Present value of future lease payments		36
Less: Lease liabilities, current		(12	)
Lease liabilities, non-current	$	24

For the years ended December 31, 2025 and 2024, the weighted-average remaining operating lease terms and the weighted-average discount rates used to determine the lease liability were as follows:


	Year Ended December 31,
	2025			2024
Weighted-average remaining lease term (in years)		4			4
Weighted-average discount rate		10.0	%		10.1	%

Intangible Assets, Net - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended				48 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2020	Dec. 31, 2025
Finite Lived Intangible Assets Line Items
Upfront payment and milestones achieved					$ 63
Acquired Finite Lived Intangible Assets Weighted Average Useful Life	9 years
Regulatory milestone payments achieved	$ 9	$ 30
Cost of sales
Finite Lived Intangible Assets Line Items
Costs of sales related to amortization of intangible asset	$ 8	$ 6	$ 4
Dimension
Finite Lived Intangible Assets Line Items
Intangible assets, remaining amortization period	6 years				6 years
Regulatory milestone payments achieved				$ 5

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets.

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-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482686/350-30-45-1

Reference 32: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
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-URI https://asc.fasb.org/1943274/2147482665/350-30-50-2

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-3

Reference 34: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-2

Reference 35: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483154/926-20-50-5

+ Details

License and Research Agreements (Tables)

12 Months Ended

Dec. 31, 2025

Share of Collaboration and Royalty Revenue Related to Crysvita

Total Crysvita revenue was as follows (in millions):


	Year Ended December 31,
	2025		2024		2023
Product sales	$	177	$	135	$	75
Revenue in Profit-Share Territory:
Royalty revenue		192		174		113
Non-cash royalty revenue		83		75		49
Collaboration revenue		—		—		70
Total revenue in Profit-Share Territory		275		249		232
Non-cash royalty revenue in European Territory		29		26		21
Total Crysvita revenue	$	481	$	410	$	328

Kyowa Kirin Collaboration

Schedule of Cost Sharing Payments

These amounts were recognized in the Company’s Consolidated Statements of Operations in connection with the collaboration agreement with KKC as follows (in millions):


	Year Ended December 31,
	2025			2024			2023
Research and development	$	(5	)	$	(4	)	$	(7	)
Selling, general and administrative	$	—		$	(4	)	$	(17	)
Cost of sales	$	61		$	46		$	18

Regeneron Pharmaceuticals Inc

Schedule of Cost Sharing Payments

These amounts were recognized in the Company’s Consolidated Statements of Operations in connection with the collaboration agreement with Regeneron as follows (in millions):


	Year Ended December 31,
	2025		2024			2023
Research and development	$	1	$	(3	)	$	8
Cost of sales	$	16	$	8		$	1

Revenue - Schedule of Sales-Related Accruals and Allowances (Details) - Product sales - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation Of Revenue [Line Items]
Balance of product sales reserve at beginning of year	$ 33	$ 17	$ 11
Provisions	50	38	19
Payments	(30)	(21)	(13)
Adjustments	4	(1)	0
Balance of product sales reserve at end of year	$ 57	$ 33	$ 17

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-5

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (a)
-Publisher FASB
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Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
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-Section 55
-Paragraph 91
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
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-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
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-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
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-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 91
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479777/606-10-55-91

+ Details

License and Research Agreements - Regeneron - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended			48 Months Ended
	Jan. 31, 2022	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2025
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Regulatory milestone payments achieved		$ 9	$ 30
Cost of sales		109	77	$ 45
Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payments of collaboration	$ 30
Regulatory milestone payments achieved					$ 33
Eligible future milestone payments		31			31
Accrued collaboration payables		$ 9	$ 18		$ 9
Maximum \| Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales	40.00%
Minimum \| Regeneron Pharmaceuticals Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profit loss sharing percentage on net sales	20.00%

Revenue (Tables)

12 Months Ended

Dec. 31, 2025

Revenue from Contract with Customer [Abstract]

Summary of Disaggregation of Total Revenues

The following table disaggregates total revenues from external customers by product sales, royalty revenue, and collaboration and license revenue (in millions):


	Year Ended December 31,
	2025		2024		2023
Product sales:
Crysvita	$	177	$	135	$	75
Dojolvi		96		88		71
Evkeeza		59		32		4
Mepsevii		37		30		30
Total product sales		369		285		180
Crysvita royalty revenue		304		275		183
Collaboration and license revenue:
Crysvita collaboration revenue in Profit-Share Territory		—		—		70
Other		—		—		1
Total collaboration and license revenue		—		—		71
Total revenues	$	673	$	560	$	434

The following table disaggregates total revenues based on geographic location (in millions):


	Year Ended December 31,
	2025		2024		2023
North America	$	377	$	340	$	307
Latin America		170		131		77
Europe, Middle East, and Africa		108		80		48
Asia-Pacific		18		9		2
Total revenues	$	673	$	560	$	434

Schedule of Sales-Related Accruals and Allowances

The following table presents the activity and ending balances for product sales related accruals and allowances (in millions):


	Year Ended December 31,
	2025			2024			2023
Balance of product sales reserve at beginning of year	$	33		$	17		$	11
Provisions		50			38			19
Payments		(30	)		(21	)		(13	)
Adjustments		4			(1	)		—
Balance of product sales reserve at end of year	$	57		$	33		$	17

Income Taxes - Effective Tax Rate of Provision for Income Taxes from Federal Statutory Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	$ (120)
Federal statutory income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit			0.80%
Federal tax credits		10.80%	7.30%
Foreign tax effects	$ 5
Foreign tax effects	(0.90%)
Effect of cross-border tax laws	$ 5
Effect of cross-border tax laws	(0.90%)
Research tax credit	$ (12)
Research tax credit	2.10%
Orphan drug credit	$ (32)
Orphan drug credit	5.60%
Change in valuation allowance	$ 145
Change in valuation allowance	(25.40%)	(27.10%)	(24.10%)
Share-based payment awards	$ 14
Share-based payment awards	(2.50%)
Stock-based compensation		(1.60%)	(1.80%)
Other	$ (1)
Other	0.30%	0.10%	(0.70%)
Nondeductible permanent items		(1.10%)	(0.30%)
Uncertain tax positions		(2.00%)	(1.40%)
Foreign rate differential		(0.40%)	(0.50%)
Provision for income taxes	$ 4	$ 2	$ (2)
Provision for income taxes	(0.70%)	(0.30%)	0.30%

License and Research Agreements - GeneTx Biotherapeutics LLC - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Regulatory milestone payments achieved	$ 9	$ 30
Future milestones payable	75
GeneTx [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible future milestone payments	85
Texas AM University [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Clinical milestone aggregate	1
Collaboration payables	0	$ 1
Texas AM University [Member] \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future contingent milestone payments	23
Annual license fee payment	$ 2

Leases - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Lessee Disclosure [Abstract]
Operating lease extension details	multiple renewal periods
Operating lease, existence of option to extend	true
Operating lease expiry term	2031
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets, Noncurrent	Other Assets, Noncurrent
Right-of-use lease assets	$ 23	$ 26
Cash paid for measurement of operating lease liabilities	$ 14	$ 16	$ 13

Balance Sheet Components - Summary of Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Inventory, Net [Abstract]
Work-in-process	$ 27	$ 22
Finished goods	25	23
Total inventory	$ 52	$ 45

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2025

Investments, Debt and Equity Securities [Abstract]

Summary of Cash Equivalents and Marketable Securities Classified as Available For Sale Securities

The fair values of cash equivalents and marketable securities classified as available-for-sale securities consist of the following (in millions):


	December 31, 2025
	Amortized		Gross Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Money market funds	$	320	$	—	$	—	$	320
Time deposits		10		—		—		10
Corporate bonds		263		—		—		263
Commercial paper		37		—		—		37
U.S. Government Treasury and agency securities		35		—		—		35
Total	$	665	$	—	$	—	$	665


	December 31, 2024
	Amortized		Gross Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Money market funds	$	114	$	—	$	—	$	114
Time deposits		10		—		—		10
Corporate bonds		391		1				392
Commercial paper		21		—		—		21
U.S. Government Treasury and agency securities		159		—		—		159
Total	$	695	$	1	$	—	$	696

Summary of Inventory

Inventory consists of the following (in millions):


	December 31,
	2025		2024
Work-in-process	$	27	$	22
Finished goods		25		23
Total inventory	$	52	$	45

Summary of Property, Plant and Equipment, Net

Property, plant, and equipment, net consists of the following (in millions):


		December 31,
	Useful life (years)	2025			2024
Building	20-30	$	182		$	182
Leasehold improvements	Shorter of lease term or estimated useful life		55			58
Research and development equipment	5		65			60
Furniture and office equipment	5		7			6
Computer equipment and software	3-5		16			16
Manufacturing equipment	5-15		37			37
Land	Not applicable		17			17
Other	Varies by asset		1			2
Property, plant, and equipment, gross			380			378
Less: accumulated depreciation			(136	)		(112	)
Property, plant, and equipment, net		$	244		$	266

Summary of Accrued Liabilities

Accrued liabilities consist of the following (in millions):


	December 31,
	2025		2024
Research and clinical study expenses	$	23	$	24
Payroll and related expenses		89		94
Revenue related reserves		57		33
Manufacturing and related expenses		67		25
Commercial and development milestones		5		45
Other		24		20
Total accrued liabilities	$	265	$	241

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

+ Details

Accumulated Other Comprehensive (Loss) Income (Tables)

12 Months Ended

Dec. 31, 2025

Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule of Total Accumulated Other Comprehensive (Loss) Income

Total accumulated other comprehensive income (loss) consisted of the following (in millions):


	Year Ended December 31,
	2025		2024
Cumulative foreign currency translation adjustment	$	1	$	(2	)
Unrealized gain on securities available-for-sale		—		1
Total accumulated other comprehensive income (loss)	$	1	$	(1	)

19.

Subsequent Events

substantially all of which are expected to be recognized during the first half of 2026. Cash payments related to these costs are expected to be made over the same period.