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Stock Incentive Plans | 3 Months Ended
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Mar. 31, 2026
Share-Based Payment Arrangement [Abstract] |
Stock Incentive Plans | Stock Incentive Plans In June 2016, the Company’s stockholders approved the 2016 Incentive Award Plan, or the 2016 Plan, which initially authorized 40,341 shares of common stock for future issuance under the 2016 Plan. Pursuant to the terms of the 2016 Plan, the Board of Directors is authorized to grant awards with respect to common stock, and may delegate to a committee of one or more members of the Board of Directors or executive officers of the Company the authority to grant options and restricted stock units. The Board of Directors established a Stock Option Committee which is authorized to grant awards to certain employees and consultants subject to conditions and limitations within the 2016 Plan. In January 2026, the number of shares of common stock that may be issued under the 2016 Plan was increased by 1,040,444. As of March 31, 2026, 3,044,044 shares remain available for future issuance under the 2016 Plan. In September 2018, the Company’s 2018 Employment Inducement Incentive Award Plan, or the 2018 Inducement Incentive Award Plan, was adopted by the Board of Directors without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Stock Market LLC listing rules, which initially authorized 39,166 shares of its common stock for issuance. As of March 31, 2026, there are 502,296 shares available for future grant under the 2018 Inducement Incentive Award Plan. On November 2023, the Company assumed the 2016 Stock Incentive Plan, or the Old Cartesian Plan, of the then private company that merged with the Company in November 2023, or Old Cartesian. . The Old Cartesian Plan permits the granting of options or restricted stock to employees, officers, directors, consultants and advisors to the Company. The unvested common stock options and Series A Preferred Stock options assumed by the Company generally vest over a four-year period. Additionally, the stock options granted have a contractual term of ten years and only full shares can be exercised as per the individual award agreements. As of March 31, 2026, there are 49,149 shares available for future grant under the Old Cartesian Plan. The outstanding stock options to purchase Old Cartesian common stock were converted into stock options to purchase 776,865 shares of common stock and 14,112.299 shares of Series A Preferred Stock of the Company. The replacement awards that were issued as a part of the assumption of the Old Cartesian Plan resulted in $2.6 million attributed to post-combination service to be recognized as stock-based compensation expense over the remaining terms of the replacement awards, of which $0.1 million and $0.2 million was recognized during the three months ended March 31, 2026 and 2025, respectively as research and development expense in the consolidated statements of operations and comprehensive loss. Stock-Based Compensation Expense Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive loss, was as follows (in thousands):
| Three Months Ended March 31, |  |
| 2026 |  | 2025 |  |  |  |
Research and development | $ | 949 |  |  | $ | 1,275 |  |  |  |  |
General and administrative | 1,474 |  |  | 1,233 |  |  |  |  |
Total stock-based compensation expense | $ | 2,423 |  |  | $ | 2,508 |  |  |  |  |
Stock Options The estimated grant date fair values of stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model based on the following weighted-average assumptions:
| Three Months Ended March 31, |  |
| 2026 |  | 2025 |  |  |  |
Risk-free interest rate | 3.93 | % |  | 4.46 | % |  |  |  |
Dividend yield | — |  |  | — |  |  |  |  |
Expected term (in years) | 5.97 |  | 6.20 |  |  |  |
Expected volatility | 92.71 | % |  | 97.44 | % |  |  |  |
Weighted-average fair value of common stock | $ | 6.81 |  |  | $ | 17.46 |  |  |  |
The expected term of the Company’s stock options granted has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Under the simplified method, the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. Expected volatilities are based on the Company’s historical volatility. The weighted-average grant date fair value of stock options granted during the three months ended March 31, 2026 and 2025 was $5.25 and $14.03, respectively. As of March 31, 2026, total unrecognized compensation expense related to unvested common stock options was $15.5 million, which is expected to be recognized over a weighted average period of 3.0 years. The following table summarizes the stock option activity under the 2016 Plan, the 2018 Inducement Incentive Award Plan, and the Old Cartesian Plan for options for common stock:
| Number of Common Stock Options |  | Weighted-average Exercise Price ($) |  | Weighted-average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2025 | 2,463,747 |  |  | $ | 13.72 |  |  | 6.41 |  | $ | 2,962 |
Granted | 1,304,450 |  |  | $ | 6.81 |  |  |  |  |
Exercised | (86,132) |  |  | $ | 3.25 |  |  |  |  |
Forfeited | (139,658) |  |  | $ | 15.90 |  |  |  |  |
Outstanding at March 31, 2026 | 3,542,407 |  |  | $ | 11.34 |  |  | 7.74 |  | $ | 2,002 |
Vested at March 31, 2026 | 1,204,110 |  |  | $ | 11.35 |  |  | 5.11 |  | $ | 1,926 |
Vested and expected to vest at March 31, 2026 | 3,139,038 |  |  | $ | 11.33 |  |  | 7.64 |  | $ | 2,002 |
Restricted Stock Units During the three months ended March 31, 2026, the Company granted 420,650 restricted stock unit awards with a weighted-average fair value of $6.76 per share based on the closing price of the Company’s common stock on the date of grant under the 2016 Plan, which generally vest over a four-year term. Forfeitures are estimated at the time of grant and are adjusted, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company has estimated a forfeiture rate of 10% for restricted stock unit awards based on historical experience. Unrecognized compensation expense related to the restricted stock units was $6.4 million as of March 31, 2026, which is expected to be recognized over a weighted-average period of 3.1 years. The following table summarizes the Company’s restricted stock units under the 2016 Plan and the Old Cartesian Plan:
| Number of Shares |  | Weighted-average Grant Date Fair Value ($)
Unvested at December 31, 2025 | 522,498 |  |  | $ | 18.44 |
Granted | 420,650 |  |  | 6.76 |
Vested | (169,278) |  |  | 18.59 |
Forfeited | (37,598) |  |  | 16.61 |
Unvested at March 31, 2026 | 736,272 |  |  | $ | 11.82 |

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