11. Stock-based compensation

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2014 Stock Option and Grant Plan

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In January 2014, the Company adopted the 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it could grant incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of common stock to employees, officers, directors and consultants of the Company.

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The terms of stock option agreements, including vesting requirements, were determined by the board of directors and were subject to the provisions of the 2014 Plan. Restricted stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Stock options granted to employees generally vest over four years, with 25% vesting on the one-year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Stock options granted to non-employee consultants generally vest monthly over a period of one to four years.

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2015 Stock Option Plan

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In October 2015, the Company’s board of directors and stockholders approved the 2015 Stock Option and Incentive Plan (“2015 Stock Option Plan”), which became effective upon the completion of the Company’s initial public offering (“IPO”). The 2015 Stock Option Plan provides the Company with the flexibility to use various equity-based incentive and other awards as compensation tools to motivate its workforce. These tools include stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance share awards and cash-based awards. The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (a) 1,311,812 shares of common stock and (b) the number of shares under the 2014 Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company’s issued and outstanding shares of common stock immediately preceding December 31.

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2025 Stock Option Plan

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On March 18, 2025, the Company’s board of directors adopted, and on June 3, 2025, the stockholders approved, the 2025 Stock Incentive Plan (the “2025 Stock Option Plan”). Under the 2025 Stock Option Plan, the Company may issue awards for up to a number of shares of common stock equal to the sum of: (i) 3,631,952 shares of common stock; and (ii) such additional number of shares of common stock (up to 14,190,976 shares) as is equal to the sum of (x) the number of shares of common stock reserved for issuance under the 2015 Stock Option Plan that remained available for grant thereunder immediately prior to the date that the 2025 Stock Option Plan was approved by the Company’s stockholders and (y) the number of shares of common stock subject to awards granted under the 2015 Stock Option Plan that were outstanding as of the date that the 2025 Stock Option Plan was approved by the Company’s stockholders and which awards expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right (subject, however, in the case of incentive stock options, to any limitations under the Internal Revenue Code of 1986, as amended, and any regulations thereunder).

The Company intends to utilize the 2025 Stock Option Plan to grant equity awards to the Company’s employees, non-employee directors, consultants, and advisors in order to recruit, incentivize, retain and reward those who are critical to the Company’s success. No new awards will be granted under the 2015 Stock Option Plan.

During the year ended December 31, 2025, the Company granted options to purchase 2,302,270 shares of common stock to employees and directors under the 2025 Stock Option Plan. Additionally, the Company granted 1,854,011 restricted stock units to employees under the 2025 Stock Option Plan.

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As of December 31, 2025, there were 7,115,477 shares available for future issuance under the 2025 Stock Option Plan.

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2015 Employee Stock Purchase Plan

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In October 2015, the Company’s board of directors and stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). Under the 2015 ESPP, all full-time employees of the Company are eligible to purchase common stock of the Company twice per year, at the end of each six-month payment period. During each payment period, eligible employees who so elect, may authorize payroll deductions in an amount of 1% to 10% (whole percentages only) of the employee’s base pay for each payroll period. At the end of each payment period, the accumulated deductions are used to purchase shares of common stock from the Company at a discount. A total of 262,362 shares of common stock were initially authorized for issuance under this plan.

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On March 18, 2025, the Company’s board of directors adopted, and on June 3, 2025, the stockholders approved, the Amended and Restated 2015 Employee Stock Purchase Plan (together with the 2015 ESPP, the “ESPP”) to (i) eliminate the evergreen provision in the 2015 ESPP and (ii) expand the class of eligible employees by eliminating the requirement that participants must have completed six months of employment.

The Company issued 201,404 and 148,069 shares of common stock under the ESPP in the years ended December 31, 2025 and 2024. As of December 31, 2025, there were 1,809,493 shares available for future purchase under the ESPP.

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Inducement Awards

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During the years ended December 31, 2024 and 2023, the Company issued non-statutory stock options to purchase an aggregate of 486,000 and 573,000 shares of the Company’s common stock and restricted stock unit awards for an aggregate of 223,000 and 318,500 shares of the Company’s common stock, respectively, in each case outside of the Company’s 2015 Stock Option Plan and its 2025 Stock Option Plan as an inducement material to certain individuals’ acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). The Company did not issue any non-statutory stock options or restricted stock unit awards outside the Company’s 2015 Stock Option Plan and its 2025 Stock Option Plan during the year ended December 31, 2025. The stock options will vest over a four-year period, with 25% of the shares underlying the option award vesting on the first anniversary of the award and the remaining 75% of the shares underlying the award vesting monthly thereafter over the subsequent 36-month period. The restricted stock units vest over a three-year period, with 33% of the restricted stock units vesting on the first anniversary of the award, 33% of the restricted stock units vesting on the second anniversary, and the remaining restricted stock units vesting on the third anniversary.

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Stock-based Compensation Expense

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Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive (loss) income is as follows:

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Restricted Stock Units and Performance Restricted Stock Units

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A summary of the status of and changes in restricted stock unit, or RSU, and performance-based restricted stock unit, or PRSU, activity under the Company’s equity award plans for the year ended December 31, 2025, was as follows:

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Stock-based compensation for restricted stock units is based on the fair value of the Company’s common stock on the date of grant and is recognized over the vesting period. The restricted stock units granted during the year will vest in equal amounts, annually, over three years.

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As of December 31, 2025, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units (excluding PRSUs) of $5.8 million, which is expected to be recognized over the remaining weighted average vesting period of 1.7 years.

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During the year ended December 31, 2025, in connection with the Company’s annual compensation cycle, the Company also granted PRSUs to members of the Company’s senior leadership team to more closely align with long-term performance incentives. The awards vest as to a certain number of PRSUs upon the achievement of specified clinical performance milestones over multiple years. Stock-based compensation for PRSUs is based on the fair value of the Company’s common stock on the date of grant and will be recognized at the time the achievement of the specified performance milestones becomes probable. The Company did not recognize any stock-based compensation expense in connection with the PRSUs during the year ended December 31, 2025.

As of December 31, 2025, the Company had unrecognized stock-based compensation expense related to its unvested PRSUs of $2.6 million. The Company will recognize a cumulative catch-up adjustment in the period in which the specified performance condition is considered probable.

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Stock Options

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A summary of the status of, and changes in, stock options was as follows:

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Using the Black-Scholes option pricing model, the weighted average fair value of options granted during the years ended December 31, 2025, 2024, and 2023, was $2.82, $5.45, and $6.12, respectively.

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

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As of December 31, 2025, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $11.9 million which is expected to be recognized over the remaining weighted average vesting period of 2.3 years.