Stock-based compensation

6 Months Ended

Jun. 30, 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				Six Months Ended
	June 30,				June 30,
	2024		2023		2024		2023
	(in thousands)
Research and development	$	1,626	$	690	$	2,906	$	1,553
General and administrative		2,416		1,982		4,709		3,677
Total stock-based compensation expense	$	4,042	$	2,672	$	7,615	$	5,230

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				Six Months Ended
	June 30,				June 30,
	2024		2023		2024		2023
	(in thousands)
Stock options	$	2,577	$	1,903	$	4,985	$	3,566
Restricted stock awards and units		1,382		724		2,471		1,565
Employee stock purchase plan awards		83		45		159		99
Total stock-based compensation expense	$	4,042	$	2,672	$	7,615	$	5,230

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 six months ended June 30, 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	851,908	$	8.16
Vested	(381,069)	$	6.06
Forfeited	(38,196)	$	6.51
Unvested restricted stock units as of June 30, 2024	1,803,540	$	7.49

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. All of the restricted stock units granted in the six months ended June 30, 2024 vest in equal amounts, annually over three years. The stock-based compensation expense related to restricted stock units was $1.4 million and $2.5 million for the three and six months ended June 30, 2024, respectively. The stock-based compensation expense related to restricted stock units was $0.7 million and $1.6 million for the three and six months ended June 30, 2023, respectively.

As of June 30, 2024, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $11.1 million, which is expected to be recognized over the remaining average vesting period of 2.3 years.

Stock Options

The following is a summary of stock option activity for the six months ended June 30, 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	1,999,926	$	7.81
Exercised	(58,458)	$	4.47
Cancelled or forfeited	(500,794)	$	14.40
Outstanding at June 30, 2024	8,866,118	$	8.05	7.4		9,481
Exercisable at June 30, 2024	4,212,635	$	8.57	6.4	$	5,862

As of June 30, 2024, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $22.0 million which is expected to be recognized over the remaining weighted-average vesting period of 2.8 years.