11. Stock-based compensation

2023 stock option and grant plan (as amended and restated)

The Company adopted the 2023 Stock Option and Grant Plan (as amended and restated, the “2023 Plan”) on August 18, 2023. The 2023 Plan remained in effect until June 17, 2026. The 2023 Plan provided for the grant of incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards and restricted stock units to the employees, directors and consultants of the Company. The option exercise price of each option was determined by the administrator of the 2023 Plan and could not be less than 100% of the fair market value of the Company’s common stock on the date of grant, or in the case of an incentive stock option granted to a 10% owner, the exercise price could not be less than 110% of the fair market value of the Company’s common stock on the date of grant. The maximum term of the options granted under the 2023 Plan was no more than ten years. Service-based awards generally vest at 25% one year from the vesting commencement date and ratably each month thereafter for a period of 36 months, subject to continuous service. Performance and market-based awards would have individual vesting conditions. The shares of common stock underlying any awards that are forfeited, cancelled, reacquired by the Company prior to vesting, satisfied without the issuance of stock, or otherwise terminated (other than by exercise), or held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding under the 2023 Plan were added back to the shares of common stock available for issuance under the 2023 Plan and, following June 17, 2026, will be added back to the shares of common stock available for issuance under the 2026 Plan.

2026 stock option and incentive plan

The Company adopted the 2026 Stock Option and Incentive Plan (the "2026 Plan") on June 17, 2026, upon the cessation of the 2023 Plan. The 2026 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights ("SARs"), restricted stock awards, restricted stock units, and cash or other stock-based awards to the employees, directors, consultants and other service providers of the Company, provided that incentive stock options may be granted only to employees. The option exercise price of each option will be determined by the administrator of the 2026 Plan and shall not be less than 100% of the fair market value of the Company's common stock on the date of grant, or in the case of an incentive stock option granted to a 10% owner, the exercise price shall not be less than 110% of the fair market value of the Company's common stock on the date of grant. The maximum term of the options granted under the 2026 Plan shall not be more than ten years. Service-based awards generally vest at 25% one year from the vesting commencement date and ratably each month thereafter for a period of 36 months, subject to continuous service. Performance and market-based awards will have individual vesting conditions. Shares subject to 2023 Plan or 2026 Plan awards that are forfeited, cancelled, reacquired by the Company prior to vesting, satisfied without the issuance of stock, or otherwise terminated (other than by exercise), or held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, will be added (or added back) to the shares of common stock available for issuance under the 2026 Plan.

A total of 10,620,000 shares of common stock were initially reserved for issuance under the 2026 Plan, and such reserve will automatically increase on January 1 of each year, beginning January 1, 2027, by the lesser of (i) 5% of the total shares of common stock outstanding (including shares issuable upon exercise of any outstanding pre-funded warrants with a nominal exercise price) as of the immediately preceding December 31, or (ii) a smaller number of shares as determined by the Company's board of directors or compensation committee.

As of June 30, 2026, the Company had reserved 10,620,000 shares of common stock for issuance under the 2026 Plan. As of June 30, 2026, the number of shares remaining for grant under the 2026 Plan were 8,469,613 shares.

2026 employee stock purchase plan

On June 17, 2026, the Company adopted the 2026 Employee Stock Purchase Plan (the "ESPP"), which permits participants to contribute up to 15% of their eligible compensation during defined rolling six-month periods to purchase the Company’s common stock. The purchase price of the shares will be 85% of the lower of the fair market value of the Company’s common stock on the first day of trading of the offering period or on the applicable purchase date.

A total of 1,180,000 shares of common stock were initially reserved for issuance under the ESPP, and such reserve will increase on January 1 of each year, beginning January 1, 2027, by the least of (i) 2,360,000 shares of common stock, (ii) 1% of the shares of common stock outstanding as of the immediately preceding December 31, or (iii) such lesser number of shares as determined by the compensation committee.

As of June 30, 2026, the Company has not issued any shares under the ESPP.

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock.

Performance-based and market-based options

In June 2024, the Company’s Chief Executive Officer was granted an early-exercisable non-qualified option to purchase up to 4,277,389 shares of the Company’s common stock at a price per share of $1.35. The options vest contingent upon the satisfaction of the service, performance and market conditions. The service condition is satisfied if the optionee maintains continuous service as the Company’s Chief Executive Officer through June 6, 2027. The market condition is structured in five tranches, under which certain percentage of the options vest upon the Company achieving market valuation thresholds at specified levels. The performance condition applies only to 932,676 shares and is satisfied upon the occurrence of specified acquisition by a predetermined date. This performance condition has been met upon the closing of the license agreement with BMS (refer to Note 5, “Acquisitions and Licensing Agreements”).

In October 2025, the Company’s Chief Executive Officer was granted an early-exercisable non-qualified option to purchase up to 1,400,974 shares of the Company’s common stock at the price per share of $5.80, with vesting tied to specific service and market conditions. The service condition is satisfied if the optionee maintains continuous service as the Company’s Chief Executive Officer through June 6, 2027. The market condition is structured in four tranches, under which certain percentage of the options vest upon the Company achieving market valuation thresholds at specified levels.

In April 2026, the Company’s Chief Executive Officer was granted an early-exercisable non-qualified option to purchase up to 7,268,112 shares of the Company’s common stock at the price per share of $9.42, with vesting tied to specific service and market conditions. The service condition is satisfied if the optionee maintains continuous service relationship with the Company. The market condition is structured in four tranches, under which certain percentage of the options vest upon the Company achieving market valuation thresholds at specified levels.

The fair value of these awards was determined using a Monte Carlo simulation. The valuation assumptions utilized in the Monte Carlo model are generally consistent with the inputs discussed in the valuation of stock options below, except for volatility ranging from 80.0% to 90.0% and expected term of 9.0 to 10.0 years.

No options vested, and no options were exercised as of and for the six months ended June 30, 2026 and 2025.

Early exercise liability

The Company's equity plans allow for the early exercise of all stock options granted if authorized by the Company's board of directors at the time of grant. Any shares of common stock issued from the early exercise of stock options are restricted and vest over time. The Company has the option to repurchase any unvested shares at the lower of the original issue price or current fair value upon any voluntary or involuntary termination of such optionee. For accounting purposes, the early exercise of options is not considered to be a substantive exercise until the underlying awards vest and are not considered to be outstanding until those shares vest. The early-exercise liability is included within other non-current liabilities on the condensed consolidated balance sheets.

As of June 30, 2026 and December 31, 2025, unvested shares issued under early exercise provisions and subject to repurchase by the Company totaled 953,572 and 1,173,066, respectively, with related liabilities of $1.4 million and $1.7 million, respectively, included in other non-current liabilities.

Restricted stock activity

The Company’s equity plans allow for the grant of restricted stock awards and restricted stock units to certain employees, executives, non-employee scientific advisors, and third-party service providers. The restrictions lapse over time primarily according to service-based vesting conditions of each award. In the event of a voluntary or involuntary termination of the holder’s continuous provision of services to the Company, any unvested portion of the restricted stock award is automatically forfeited.

During six months ended June 30, 2026, the Company granted a total of 2,205,481 restricted stock units, including 78,748 restricted stock units subject to both service-based and performance-based vesting conditions (the performance condition was satisfied upon the Company's IPO in June 2026), and 2,126,733 restricted stock units granted to certain employees and directors that vest in full on the two-year anniversary of the grant date, subject in each case to the applicable continued service relationship through the vesting date.

Modification of Chief Medical Officer Restricted Stock Award

The original vesting terms of the Chief Medical Officer’s award of 3,982,000 shares granted in August 2023 provided for 80% of the shares to vest immediately, with the remaining 20% vesting in equal monthly installments over a 24-month period.

On June 6, 2024, in connection with the Company’s Series A financing and adoption of the 2023 Plan, the Company revised the vesting terms of the award to provide for 50% immediate vesting, with the remaining 50% vesting monthly over 36 months from the new vesting commencement date. The Company determined that this was an escrowed share arrangement under ASC 718 and determined that the shares were a new compensatory award. The incremental compensation cost of $7.8 million was measured as the excess of the fair value of the modified award over the fair value of the original award immediately prior to modification, to be recognized over a 36-month service period starting on June 6, 2024. For purposes of the net loss per share calculation, the Company determined that the modification is equivalent to a reverse stock split and, accordingly, adjusted the weighted-average number of unvested restricted stock shares under the Chief Medical Officer’s award as if those terms had been in effect for all periods presented.

Stock-based compensation expense

As of June 30, 2026, unrecognized stock-based compensation expense related to unvested awards totaled $159.2 million, which is expected to be recognized over a weighted-average period of 2.72 years.