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Stock-Based Compensation | 9 Months Ended
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Sep. 30, 2025
Share-Based Payment Arrangement [Abstract] |
Stock-Based Compensation |
7. | Stock-Based Compensation
The 2023 Stock Option and Incentive Plan (2023 Plan) was adopted by the board of directors, approved by the Company’s stockholders on July 4, 2023, and became effective on July 13, 2023, replacing the 2017 Equity Incentive Plan. The number of shares initially reserved for issuance under the 2023 Plan was 2,585,968. The number of shares will automatically increase each January 1, by (i) 4% of the outstanding number of shares of the Company’s Series A common stock on the immediately preceding December 31 or (ii) a lesser number of shares as determined by the compensation committee of the board of directors. In accordance with the 2023 Plan, the shares reserved for issuance automatically increased by 855,016 shares on January 1, 2024, and by 1,226,994 shares on January 1, 2025. As of September 30, 2025, the aggregate maximum number of shares reserved for issuance under the 2023 Plan was 4,667,978, of which 1,426,290 shares were available for future grants. Option grants issued under the 2023 Plan are exercisable for up to 10 years from the date of issuance. In March 2024, the Company established a pool of 1,000,000 shares of Series A common stock (Inducement Pool) from which equity grants in the form of options and restricted stock units may be issued as inducement for new employees to accept employment offers from the Company or for individuals returning to employment after a bona fide period of non-employment with the Company. Inducement Pool grants are granted outside of the 2023 Plan and do not require approval from the Company’s stockholders pursuant to the Nasdaq inducement grant exception in accordance with Nasdaq Listing Rule 5635(c)(4). In February 2025, the Company increased the number of shares available for issuance by 300,000 shares, increasing the total number of shares available for issuance under the Inducement Pool to 1,300,000 shares. As of September 30, 2025, 404,017 shares were available for future grants from the Inducement Pool. Total stock-based compensation recorded in the condensed statements of operations and comprehensive loss related to stock options and restricted stock units for employees and non-employees was as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended September 30, |  | Nine Months Ended September 30,
​ | ​ | 2025 |  | 2024 | ​ | 2025 | ​ | 2024
Stock options | ​ | $ | 1,402 | ​ | $ | 1,316 | ​ | $ | 3,941 | ​ | $ | 2,903
Restricted stock units | ​ |  | 286 | ​ |  | 230 | ​ |  | 817 | ​ |  | 851
Total stock-based compensation expense | ​ | $ | 1,688 | ​ | $ | 1,546 | ​ | $ | 4,758 | ​ | $ | 3,754
Included in: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
General and administrative expense | ​ | $ | 1,454 | ​ | $ | 1,311 | ​ | $ | 4,068 | ​ | $ | 3,005
Research and development expense | ​ |  | 234 | ​ |  | 235 | ​ |  | 690 | ​ |  | 749
Total stock-based compensation expense | ​ | $ | 1,688 | ​ | $ | 1,546 | ​ | $ | 4,758 | ​ | $ | 3,754
​ Stock options ​ The Company grants stock options which consist of (i) time-based options, which vest and become exercisable, subject to the participant’s continued employment or service through the applicable vesting date and (ii) performance-based options, which vest based on performance measures against predetermined objectives that include successful completion of qualified equity offerings or announced topline results for clinical trials and positive clinical results over a specified performance period. The Company’s time-based options have various vesting schedules that range from vesting immediately to vesting over a four-year period. The following table summarizes stock option activity for the nine months ended September 30, 2025 (in thousands, except share and per share data):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted- |  | ​ | ​
​ | ​ | Number of | ​ | ​ | ​ | ​ | Average | ​ | ​ | ​
​ | ​ | Shares | ​ | Weighted- | ​ | Remaining | ​ | ​ | ​
​ | ​ | Underlying | ​ | Average | ​ | Contractual | ​ | Aggregate
​ | ​ | Outstanding | ​ | Exercise | ​ | Term | ​ | Intrinsic
​ | ​ | Options | ​ | Price | ​ | (in Years) | ​ | Value (1)
Outstanding, January 1, 2025 |  | 4,462,517 | ​ | $ | 6.58 |  | 7.4 | ​ | $ | 619
Granted |  | 1,276,597 | ​ | ​ | 4.83 |  | ​ | ​ |  | ​
Exercised | ​ | (44,792) | ​ | ​ | 6.14 | ​ | ​ | ​ | ​ | ​
Forfeited/expired |  | (147) | ​ | ​ | 23.05 |  | ​ | ​ |  | ​
Outstanding, September 30, 2025 (2) |  | 5,694,175 | ​ | $ | 6.19 |  | 7.3 | ​ | $ | 7,048
Vested and expected to vest, September 30, 2025 |  | 5,694,175 | ​ | $ | 6.19 |  | 7.3 | ​ | $ | 7,048
Exercisable at September 30, 2025 |  | 3,422,341 | ​ | $ | 6.74 |  | 6.3 | ​ | $ | 2,668
​
| (1) | Aggregate intrinsic value represents the difference between the fair value of the Company’s Series A common stock on the last day of the fiscal period and the exercise price, multiplied by the number of options outstanding.
| (2) | Includes 477,467 performance-based options with a weighted-average exercise price of $6.44, all of which were fully vested and exercisable.
During the nine months ended September 30, 2025 and 2024, the weighted average grant-date fair value per share of stock options granted was $3.77 and $3.42, respectively. The total intrinsic value of stock options exercised during the nine months ended September 30, 2025 and 2024, was $0.2 and $0.1 million, respectively. Additionally, during the nine months ended September 30, 2025 and 2024, cash received from the exercise of stock options was approximately $0.3 and $0.1 million, respectively. As of September 30, 2025, there was $9.4 million of unrecognized compensation expense, which is expected to be recognized over a remaining weighted-average period of 2.2 years. Restricted stock units The Company’s restricted stock units generally vest over a four-year period in equal amounts on an annual basis, provided the employee remains continuously employed with the Company. The fair value of the restricted stock units is equal to the closing price of the Company’s Series A common stock on the grant date. The following table summarizes restricted stock unit activity: ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted-Average
​ |  | Restricted |  | Grant Date
​ |  | Stock Units |  | Fair Value
Outstanding, January 1, 2025 |  | 844,382 | ​ | $ | 2.96
Granted |  | 254,017 | ​ | ​ | 4.71
Vested/released |  | (281,462) | ​ | ​ | 2.96
Outstanding, September 30, 2025 | ​ | 816,937 | ​ | $ | 3.50
​ As of September 30, 2025, the total unrecognized compensation expense related to unvested restricted stock units was $2.5 million, which is expected to be recognized over a remaining weighted-average period of 2.4 years. Valuation assumptions The fair value of each stock option granted was estimated on the date of grant using the Black-Scholes option pricing model using the following assumptions: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Nine Months Ended September 30,
​ | ​ | 2025 | ​ | 2024
Expected volatility |  | 95 - 96 | % | ​ | 91 - 96 | %
Risk-free interest rate |  | 4.1 - 4.3 | % | ​ | 3.9 - 4.5 | %
Dividend yield |  | — |  | ​ | — |
Expected term (in years) |  | 5.3 - 6.0 | ​ | ​ | 5.3 - 6.1 | ​
​ The expected term is determined using the simplified method, which represents the average of the contractual term of the options and the weighted-average expected vesting period. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the option. The expected stock volatility rate is based on the volatility rates of comparable publicly held companies over a period equal to the expected term of the option. The Company utilizes a dividend yield of zero based on the fact that the Company has never paid cash dividends to stockholders and has no current intentions to pay cash dividends. ​ Employee stock purchase plan ​ The 2023 Employee Stock Purchase Plan (the ESPP) was adopted by the board of directors in July 2023 with an initial total of 215,497 shares of Series A common stock reserved for issuance. Under the ESPP plan, the amount of shares reserved automatically increases each January 1 through January 1, 2033, by the least of (i) 215,497 shares of Series A common stock, (ii) 1% of the outstanding number of shares of the Company’s Series A common stock on the immediately preceding December 31 or (iii) such lesser number of shares of Series A common stock as determined by the administrator of the ESPP. In accordance with the ESPP, the shares reserved for issuance automatically increased by 213,754 shares on January 1, 2024, and by 215,497 shares on January 1, 2025. As of September 30, 2025, the aggregate maximum number of shares reserved for issuance under the ESPP was 644,748. No shares of Series A common stock have been issued under the ESPP to date.

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