Stock-Based Compensation

3 Months Ended

Mar. 31, 2024

Stock-Based Compensation

Stock-Based Compensation

(8)  Stock-Based Compensation

A summary of stock option activity for the three months ended March 31, 2024 is as follows:

		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options outstanding at December 31, 2023	6,378,924	$	29.69	7.5
Granted	5,000	$	37.08
Exercised	(222,619)	$	16.27
Canceled	(2,568)	$	83.21
Options outstanding at March 31, 2024	6,158,737	$	30.16	7.4
Options vested and expected to vest at March 31, 2024	6,065,176	$	30.14	7.3
Options exercisable at March 31, 2024	3,284,980	$	29.45	6.3
Shares available for grant under the 2021 Plan	1,011,071

The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2024 was $28.64.

The aggregate intrinsic value of stock options vested and expected to vest at March 31, 2024 was $104.1 million. The aggregate intrinsic value of stock options exercisable at March 31, 2024 was $74.3 million. As of March 31, 2024, total compensation cost related to non-vested employee, consultant and non-employee director stock options not yet recognized was approximately $55.3 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 2.4 years.

Stock-based compensation expense for the three months ended March 31, 2024 and 2023 was recorded as follows:

	Three Months Ended March 31,
	2024		2023
	(In thousands)
Research and development	$	3,693	$	2,162
General and administrative		3,509		2,178
Total stock-based compensation expense	$	7,202	$	4,340

The fair values of employee, consultant and non-employee director stock options granted during the three months ended March 31, 2024 and 2023 were valued using the Black-Scholes option pricing model with the following assumptions:

	Three Months Ended March 31,
	2024	2023
Expected stock price volatility	92%	92%
Expected option term	6.0 Years	6.0 Years
Risk-free interest rate	4.0 – 4.3%	3.7 – 4.0%
Expected dividend yield	None	None