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Stock-Based Compensation | 12 Months Ended
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Dec. 31, 2025
Share-Based Payment Arrangement [Abstract] |
Stock-Based Compensation | 9. Stock-Based Compensation 2018 Stock Option and Incentive Plan On December 12, 2018, the Company adopted the Aura Biosciences, Inc. 2018 Equity Incentive Plan, or the 2018 Plan. The 2018 Plan will expire in 2028. Under the 2018 Plan, Aura may grant incentive stock options, non-qualified stock options, restricted and unrestricted stock awards and stock rights. The Board of Directors, or the Board, has determined not to make any further awards under the 2018 Plan as of November 2, 2021. However, the 2018 Plan will continue to govern outstanding equity awards granted thereunder. 2021 Stock Option and Incentive Plan The 2021 Stock Option and Incentive Plan, or the 2021 Plan, was adopted by the Board on October 7, 2021, approved by the Company’s stockholders on October 22, 2021 and became effective on November 1, 2021. The 2021 Plan permits the granting of several award types, including restricted stock units and both options to purchase common stock intended to qualify as incentive stock options under Section 422 of the United States Internal Revenue Code, or the Code, and options that do not so qualify. The number of shares initially reserved for issuance under the 2021 Plan was 3,352,166, which increased on January 1, 2022 and will continue to increase each January 1 thereafter, by 5% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s compensation committee. The maximum number of shares of common stock that may be issued in the form of incentive stock options shall not exceed the initial limit, cumulatively increased on January 1, 2022 and on each January 1 thereafter by the lesser of the annual increase for such year or 3,352,166 shares of common stock. On January 1, 2025, the shares reserved for issuance were increased to 11,667,747 shares. With the transfer of shares to the 2021 Plan in connection with the termination or expiration of awards under the 2018 Plan, together with shares otherwise available under the 2021 Plan, there were 3,847,257 shares available for grant under the 2021 Plan at December 31, 2025. 2021 Employee Stock Purchase Plan The 2021 Employee Stock Purchase Plan, or the ESPP, was adopted by the Board on October 7, 2021, approved by the Company’s stockholders on October 22, 2021 and became effective on November 1, 2021. A total of 335,217 shares of common stock were initially reserved for issuance under this plan, which increased on January 1, 2022 and will continue to increase each January 1 thereafter through January 1, 2031, by the least of (i) 335,217 shares of common stock, (ii) 1% of the outstanding number of shares of common stock on the immediately preceding December 31 or (iii) such lesser number of shares of common stock as determined by the administrator of the ESPP. On January 1, 2025, the shares reserved for issuance were increased to 1,593,596 shares. The purchase price of the shares under the ESPP is at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the purchase date. As of December 31, 2025, 1,565,471 shares were available to be issued under the ESPP. The Company recognized $0.1 million of stock-based compensation expense related to the ESPP for each of the years ended December 31, 2025 and 2024. Stock Options The Board is authorized to administer the 2021 Plan. In accordance with the provisions of the 2021 Plan, the Board determines the terms of Aura options and other awards issued pursuant thereto, including the following: ▪ which employees, directors and consultants shall be granted awards; ▪ the number of shares of common stock subject to options and other awards; ▪ the exercise price of each option, which generally shall not be less than fair market value of the common stock on the date of grant; ▪ the termination or cancellation provisions applicable to options; ▪ the terms and conditions of other awards, including conditions for repurchase, termination or cancellation, issue price and repurchase price; and ▪ all other terms and conditions upon which each award may be granted in accordance with the 2021 Plan. In addition, the Board may award restricted shares of common stock and restricted stock units to participants subject to such conditions and restrictions as it may determine. The Board or any committee to which the Board delegates authority may, with the consent of the affected plan participants, re-price or otherwise amend outstanding awards consistent with the terms of the 2021 Plan. The following table summarizes stock option activity under the 2018 Plan and 2021 Plan for the year ended December 31, 2025:
|  | Options |  |  | Weighted- Average Exercise Price |  |  | Weighted- Average Remaining Contractual Term (years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding at December 31, 2024 |  |  | 5,522,353 |  |  | $ | 8.17 |  |  |  | 6.91 |  |  | $ | 8,068 |
Granted |  |  | 1,596,043 |  |  |  | 7.14 |  |  |  |  |  |  |
Exercised |  |  | (247,993 | ) |  |  | 4.30 |  |  |  |  |  |  |
Cancelled/Forfeited |  |  | (402,821 | ) |  |  | 10.35 |  |  |  |  |  |  |
Outstanding at December 31, 2025 |  |  | 6,467,582 |  |  | $ | 7.93 |  |  |  | 6.96 |  |  | $ | 1,503 |
Exercisable at December 31, 2025 |  |  | 3,908,454 |  |  | $ | 8.07 |  |  |  | 5.79 |  |  | $ | 1,503 |
The weighted-average grant date fair value of stock options granted during the years ended December 31, 2025 and 2024 was $5.51 and $5.99 per share, respectively. The total intrinsic value of options exercised was $0.6 million and $1.5 million for the years ended December 31, 2025 and 2024, respectively. The fair value of the stock options issued as of December 31, 2025 and 2024 was measured with the following weighted-average assumptions:
| Year Ended December 31, |
| 2025 |  |  | 2024 |
Risk-free interest rate |  | 4.26 | % |  |  | 3.93 | %
Expected term (years) |  | 6.05 |  |  |  | 6.03 |
Expected volatility of the underlying stock |  | 91.65 | % |  |  | 88.63 | %
Expected dividend rate |  | — | % |  |  | — | %
Restricted Stock Units The Company has granted restricted stock units with service-based and performance-based vesting conditions. Unvested restricted stock units may not be sold or transferred by the holder. A summary of the restricted stock units activity during the year ended December 31, 2025 is as follows:
|  | Restricted Stock Units |  |  | Weighted- Average Grant Date Fair Value |
Unvested at December 31, 2024 |  |  | 1,589,042 |  |  | $ | 8.76 |
Granted |  |  | 1,837,279 |  |  |  | 7.30 |
Vested/Released |  |  | (532,401 | ) |  |  | 9.01 |
Forfeited |  |  | (203,143 | ) |  |  | 8.46 |
Unvested at December 31, 2025 |  |  | 2,690,777 |  |  | $ | 7.74 |
During the year ended December 31, 2025, 532,401 restricted stock units vested with a fair value of $4.8 million. Stock-Based Compensation Expense The Company recorded stock-based compensation expense as follows (in thousands):
|  | Year Ended December 31, |
|  | 2025 |  |  | 2024 |
Research and development |  | $ | 7,825 |  |  | $ | 5,696 |
General and administrative |  |  | 6,492 |  |  |  | 6,026 |
Total |  | $ | 14,317 |  |  | $ | 11,722 |
As of December 31, 2025, there was $13.1 million of unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of 2.62 years. As of December 31, 2025, there was $16.2 million of unrecognized compensation expense related to restricted stock units, which is expected to be recognized over a weighted-average period of 2.68 years.

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