Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2024

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Summary of Stock Option Activity

A summary of the Company’s stock option activity under the 2021 Plan and 2018 Plan is as follows (in thousands, except share and per share data and years):

						Weighted-
				Weighted-		average remaining		Aggregate
				average		contractual		intrinsic
	Shares			exercise price		term (years)		value
Outstanding at December 31, 2023		24,970,957		$	4.98		8.12	$	4,412
Granted		11,596,445			1.76
Exercised		(145,293	)		0.89
Canceled		(1,593,563	)		3.93
Outstanding at June 30, 2024		34,828,546		$	3.97		8.05	$	11,579
Options exercisable at June 30, 2024		15,155,782		$	4.70		6.83	$	5,433

Schedule of Stock-based Compensation Expense

The allocation of stock-based compensation for all stock awards was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Research and development	$	3,788	$	3,867	$	7,272	$	7,747
General and administrative		3,392		3,145		6,756		6,110
Total	$	7,180	$	7,012	$	14,028	$	13,857

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consisted of the following as of June 30, 2024 and December 31, 2023:

	June 30,		December 31,
	2024		2023
Stock options issued and outstanding		34,828,546		24,970,957
Awards available for future grant		12,913,020		15,342,797
Shares available for purchase under the ESPP		1,828,237		2,080,681
Total		49,569,803		42,394,435

ESPP

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Assumptions used to Determine Fair Value of Stock Option Grants

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the stock to be purchased under the ESPP were as follows:

	Three Months Ended June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Risk-free interest rate	4.75%-5.39%	4.70%-5.35%	4.75%-5.39%	4.70%-5.35%
Expected volatility	68.73%-74.72%	72.54%-82.79%	68.73%-74.72%	72.54%-82.79%
Expected term (in years)	0.49-1.99	0.50-1.99	0.49-1.99	0.50-1.99
Expected dividend yield	--%	--%	--%	--%

Employee Stock Option

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Assumptions used to Determine Fair Value of Stock Option Grants

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows:

	Three Months Ended June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Risk-free interest rate	4.26%-4.64%	3.50%-3.98%	3.84%-4.64%	3.46%-4.22%
Expected volatility	82.72%-83.14%	83.20%-85.02%	82.72%-83.91%	83.20%-85.81%
Expected term (in years)	5.50-6.08	5.50-6.08	5.28-6.08	5.50-6.08
Expected dividend yield	--%	--%	--%	--%