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Fair Value Measurements
 12 Months Ended
Dec. 31, 2025
Fair Value Disclosures [Abstract]  
Fair Value Measurements Fair Value Measurements
The Company determines the fair value of financial assets and liabilities using the fair value hierarchy, which establishes three levels of inputs that may be used to measure fair value, as follows:
•Level 1: Inputs which include quoted prices in active markets for identical assets and liabilities.
•Level 2: Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices 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 assets or liabilities.
•Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
The carrying amounts of the Company’s financial instruments, including accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities.
Cash Equivalents and Available-for-Sale Securities
The following tables summarize the Company’s Level 1 and Level 2 financial assets measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands):
December 31, 2025
Valuation
Hierarchy
Amortized
Cost
Gross
Unrealized
Holding
Gains		Gross
Unrealized
Holding
Losses
Aggregate
Fair Value
Assets:
Money market fundsLevel 1$86,607 $— $— $86,607 
U.S. government treasuriesLevel 2310,148 341 (3)310,486 
U.S. government agency bonds and discount notesLevel 245,773 6 (16)45,763 
Asset-back securitiesLevel 284,676 277 — 84,953 
Corporate bondsLevel 2156,160 499 (1)156,658 
Equity securitiesLevel 1N/AN/AN/A6,077 
Total financial assets$683,364 $1,123 $(20)$690,544 
Reconciliation to cash, cash equivalents and investments on consolidated balance sheet
Minus: Restricted cash equivalents invested in money market funds(7,916)
Plus: Cash deposits98,962 
Total cash, cash equivalents and investments$781,590 
December 31, 2024
Valuation
Hierarchy		Amortized
Cost		Gross
Unrealized
Holding
Gains		Gross
Unrealized
Holding
Losses		Aggregate
Fair Value
Assets:
Money market fundsLevel 1$146,505 $— $— $146,505 
U.S. government treasuriesLevel 2588,794 722 (33)589,483 
U.S. government agency bonds and discount rates Level 238,081 17 (19)38,079 
Asset-back securitiesLevel 251,038 220 (10)51,248 
Corporate bondsLevel 2252,935 529 (9)253,455 
Equity securitiesLevel 1N/AN/AN/A4,350 
Total financial assets$1,077,353 $1,488 $(71)$1,083,120 
Reconciliation to cash, cash equivalents and investments on consolidated balance sheet
Minus: Restricted cash equivalents invested in money market funds(20,281)
Plus: Cash deposits32,524 
Total cash, cash equivalents and investments$1,095,363 
Accrued interest receivable excluded from both the fair value and amortized cost basis of the available-for-sale debt securities are presented within prepaid expenses and other current assets in the consolidated balance sheets. Accrued interest receivable amounted to $3.6 million and $5.0 million as of December 31, 2025 and 2024, respectively. The Company did not write off any accrued interest receivable during the years ended December 31, 2025, 2024 and 2023.
The Company recognized total net unrealized gains of $1.1 million and $1.4 million in accumulated other comprehensive loss as of December 31, 2025 and 2024, respectively. The gross unrealized losses as of December 31, 2025 and 2024 were due to changes in interest rates. The Company determined that the gross unrealized losses on our investments as of December 31, 2025 and 2024 were temporary in nature. The Company currently does not intend, and it is highly unlikely that it will be required, to sell these securities before recovery of their amortized cost basis. As of December 31, 2025, no securities have contractual maturities (or weighted average life for asset-backed securities) of longer than two years.
As of December 31, 2025, the Company’s equity investment consisted solely of ordinary shares of Brii Biosciences Limited (Brii Bio Parent). The equity securities of Brii Bio Parent are listed on the Stock Exchange of Hong Kong Limited and are considered to be marketable equity securities measured at fair value at each reporting date. As of December 31, 2025, the Company remeasured the equity investment at a fair value of $6.1 million. For the year ended December 31, 2025, the Company recognized unrealized gain of $1.7 million as other income in the consolidated statements of operations. For the years ended December 31, 2024 and 2023, the Company recognized unrealized losses of $5.5 million and $21.9 million, respectively, as other income in the consolidated statements of operations. For the years ended December 31, 2025, 2024 and 2023, the unrealized gains or loss related to foreign currency translation were immaterial.
Contingent Consideration
Contingent consideration primarily includes potential milestone payments in connection with the acquisitions of Humabs BioMed SA (Humabs) in 2017. The Company classifies the contingent consideration as Level 3 financial liabilities within the fair value hierarchy as of December 31, 2025 and 2024. The estimated fair value of the contingent consideration related to the Humabs acquisition was determined by calculating the probability-weighted regulatory and commercial milestone payments based on the assessment of the likelihood and estimated timing that certain milestones would be achieved.
During the three months ended March 31, 2025, the Company achieved a $17.5 million clinical milestone upon the enrollment of the first patient in phase 3 ECLIPSE registrational program for chronic hepatitis delta, which was paid in April 2025. As of December 31, 2025, the Company calculated the estimated fair value of the remaining regulatory approval milestone related to tobevibart using the following significant unobservable inputs:
Unobservable inputValue
Discount rates11.4%
Probability of achievement85.5%
For the commercial milestones, the Company used a Monte Carlo simulation because of the availability of discrete revenue forecasts. As of December 31, 2025, the Monte Carlo simulation assumed a commercial product launch and associated discrete revenue forecasts, as well as the following significant unobservable inputs for the remaining commercial milestones related to tobevibart:
Unobservable inputValue
Volatility65.0%
Discount rate11.0%
Probability of achievement85.5%
The discount rate captures the credit risk associated with the payment of the contingent consideration when earned and due. As of December 31, 2025 and 2024, the estimated fair value of the contingent consideration related to the Humabs acquisition was $34.1 million and $40.1 million, respectively, with changes in the estimated fair value recorded in research and development expenses in the consolidated statements of operations. The estimated fair value of the contingent consideration related to the Humabs acquisition involves significant estimates and assumptions, which give rise to measurement uncertainty.
The following table sets forth the changes in the estimated fair value of the Company’s contingent consideration (in thousands):
Contingent
Consideration
Balance at December 31, 2024$40,110 
Changes in fair value11,490 
Payment(17,500)
Balance at December 31, 2025$34,100