In February 2021, the Company adopted the 2021 Incentive Award Plan (2021 Plan) and the 2021 Employee Stock Purchase Plan (2021 ESPP), both of which became effective on the completion of the Company’s initial public offering. The 2021 Plan provides for a variety of stock-based compensation awards, including stock options, restricted stock awards (RSAs), and restricted stock units (RSUs). The 2021 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their earnings, subject to plan limitations. Unless otherwise determined by the Company’s board of directors, employees may purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first date of an offering period or on the purchase date. As of June 30, 2025, 33.1 million shares and 5.9 million shares were available for future issuance under the 2021 Plan and the 2021 ESPP, respectively.

Stock-based compensation expense

Stock-based compensation expense is recognized in the condensed consolidated statements of operations as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
	(in thousands)
Research and development	$	4,238	$	7,123	$	8,824	$	12,971
General and administrative		2,391		4,257		4,827		7,501
Total stock-based compensation expense	$	6,629	$	11,380	$	13,651	$	20,472

Unrecognized stock-based compensation costs related to unvested awards and the weighted-average period over which the costs are expected to be recognized as of June 30, 2025 are as follows:


	Stock Options		RSUs
Unrecognized stock-based compensation expense (in thousands)	$	33,932	$	17,095
Weighted-average period costs expected to be recognized (in years)		2.4		2.9

Stock options

A summary of the Company’s stock option activity is as follows:


	Stock Options (in thousands)			Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2024		25,062		$	7.16		7.4	$	271
Granted		5,498			2.59
Exercised		(600	)		1.87
Forfeited/Cancelled		(4,948	)		8.75
Outstanding as of June 30, 2025		25,012		$	5.99		7.6	$	2,728
Exercisable as of June 30, 2025		13,691		$	7.00		6.5	$	1,617

The fair value of stock options granted to employees, directors, and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following assumptions:


	Six Months Ended June 30,
Assumptions	2025	2024
Risk free interest rate	4.1% – 4.4%	3.8% – 4.7%
Expected volatility	75.0%	72.5%
Expected term (years)	5.43 – 6.50	5.50 – 6.25
Expected dividend	0%	0%

The following table summarizes additional information related to stock option activity:


	Six Months Ended June 30,
	2025		2024
Weighted average grant date fair value per share for options granted	$	1.79	$	6.19
Aggregate intrinsic value of stock options exercised (in thousands)	$	1,351	$	5,391

Restricted stock

A summary of the Company’s RSU activity is as follows:


	RSUs (in thousands)			RSUs Weighted-Average Grant Date Fair Value per Share
Unvested as of December 31, 2024		3,570		$	6.72
Granted		2,072			2.58
Vested		(1,163	)		5.89
Forfeited		(356	)		6.88
Unvested as of June 30, 2025		4,123		$	4.86

The fair value of RSUs that vested during the six months ended June 30, 2025 and 2024 was $2.6 million and $4.6 million, respectively.

13. Stock-based compensation

Equity incentive plans

Stock-based compensation expense

Stock options

Restricted stock