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.

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 both options to purchase common stock intended to qualify as incentive stock options under Section 422 of 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 3,769,133 options and restricted stock units available for grant under the 2021 Plan at June 30, 2025.

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 June 30, 2025, 1,578,333 shares were available to be issued under the ESPP. The Company recognized $0.01 million and $0.02 million in stock-based compensation expense related to the ESPP for the three months ended June 30, 2025 and 2024, respectively. The Company recognized $0.03 million and $0.05 million of share-based compensation expense related to the ESPP for the six months ended June 30, 2025 and 2024, respectively.

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:

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 six months ended June 30, 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		1,426,590			7.25
Exercised		(11,372	)		5.04
Cancelled/Forfeited		(76,824	)		8.29
Outstanding at June 30, 2025		6,860,747		$	7.98		7.10	$	3,451
Exercisable at June 30, 2025		3,940,802		$	7.87		5.67	$	3,393

The weighted-average grant date fair value of stock options granted during the six months ended June 30, 2025 and 2024 was $5.57 and $5.84 per share, respectively. The fair value of options vested during the six months ended June 30, 2025 and 2024 was $4.6 million and $4.3 million, respectively. The total intrinsic value of options exercised was $0.01 million and $0.4 million for the six months ended June 30, 2025 and 2024, respectively.

The fair value of the stock options granted for the three and six months ended June 30, 2025 and 2024 was measured with the following weighted-average assumptions:


	Three Months Ended June 30,						Six Months Ended June 30,
	2025			2024			2025			2024
Risk-free interest rate		4.09	%		4.37	%		4.31	%		3.93	%
Expected term (years)		6.00			5.97			6.04			6.04
Expected volatility of the underlying stock		90.80	%		89.10	%		90.87	%		88.59	%
Expected dividend rate		—	%		—	%		—	%		—	%

The Company has granted restricted stock units with service-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 six months ended June 30, 2025 is as follows:


	Restricted Stock Units			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2024		1,589,042		$	8.76
Granted		1,619,482			7.43
Vested/Released		(320,519	)		8.42
Forfeited		(63,766	)		8.24
Unvested at June 30, 2025		2,824,239		$	8.05

As a result of the 2021 Plan, the Company granted restricted stock units which vest in increments of 25% annually over a period of four years. For the six months ended June 30, 2025, 320,519 restricted stock units vested with a fair value of $2.7 million.

The Company recorded stock-based compensation expense as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	2,069	$	1,541	$	3,984	$	3,019
General and administrative		1,764		1,585		3,363		3,016
Total	$	3,833	$	3,126	$	7,347	$	6,035

As of June 30, 2025, there was $16.7 million of unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of 2.89 years.

As of June 30, 2025, there was $19.5 million of unrecognized compensation expense related to restricted stock units, which is expected to be recognized over a weighted-average period of 3.07 years.