Stock-based compensation

3 Months Ended

Mar. 31, 2024

Stock-based compensation

Stock-based compensation

9. Stock-based compensation

Stock-Based Compensation Expense

Total compensation cost recognized for all stock-based compensation awards in the condensed consolidated statements of operations and comprehensive (loss) income was as follows:

	Three Months Ended
	March 31,
	2024		2023
	(in thousands)
Research and development	$	1,280	$	863
General and administrative		2,293		1,695
Total stock-based compensation expense	$	3,573	$	2,558

Stock-based compensation expense by type of award included within the condensed consolidated statements of operations and comprehensive (loss) income was as follows:

	Three Months Ended
	March 31,
	2024		2023
	(in thousands)
Stock options	$	2,408	$	1,663
Restricted stock awards and units		1,090		841
Employee stock purchase plan awards		75		54
Total stock-based compensation expense	$	3,573	$	2,558

Restricted Stock Units

A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the three months ended March 31, 2024 was as follows:

		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2023	1,370,897	$	6.65
Granted	696,908	$	7.63
Vested	(324,520)	$	5.75
Forfeited	(23,947)	$	6.42
Unvested restricted stock units as of March 31, 2024	1,719,338	$	7.22

Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and is recognized over the vesting period. Restricted stock units granted by the Company typically vest in equal amounts, annually over three years. All of the restricted stock units granted in the three months ended March 31, 2024 vest in equal amounts, annually over three years. The stock-based compensation expense related to restricted stock units and awards was $1.1 million and $0.8 million for the three months ended March 31, 2024 and 2023, respectively.

As of March 31, 2024, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $10.9 million, which is expected to be recognized over the remaining average vesting period of 2.4 years.

Stock Options

The following is a summary of stock option activity for the three months ended March 31, 2024:

		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2023	7,425,444	$	8.52
Granted	1,747,626	$	7.68
Exercised	(32,500)	$	4.91
Cancelled or forfeited	(230,974)	$	12.28
Outstanding at March 31, 2024	8,909,596	$	8.27	7.8	$	17,875
Exercisable at March 31, 2024	3,880,357	$	9.04	6.2	$	8,728

As of March 31, 2024, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $23.2 million which is expected to be recognized over the remaining weighted-average vesting period of 3.0 years.