Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2024

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Shares of Common Stock Reserved for Issuance

Shares of common stock reserved for issuance under the Company’s equity incentive plans were as follows:

	June 30, 2024
Outstanding stock awards		9,155,525
Reserved for future award grants		5,386,630
Reserved for future ESPP		192,341
Total common stock reserved for stock awards		14,734,496

Service-Based

Summary of Stock Option Activity

A summary of the Company’s service-based stock option activity (excluding performance-based stock option activity, which is presented separately below) for the six months ended June 30, 2024 is as follows:

	Outstanding Service-Based Options
(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance—December 31, 2023		5,805,586		$	7.40		6.90	$	64
Options granted		2,924,500			1.56
Options exercised		—			—
Options forfeited or expired		(617,967	)		10.36
Balance—June 30, 2024		8,112,119		$	5.07		8.01	$	6
Options vested and exercisable as of June 30, 2024		3,663,128		$	8.19		6.49	$	—

Summary of Weighted-average Assumptions Used in Determination of Fair Value of Stock Options

	Three Months Ended June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Expected term (in years)	5.50 - 6.08	5.50 - 6.02	5.50 - 6.08	5.50 - 6.02
Volatility	72.61 - 73.12%	78.47 - 79.31%	72.61 - 80.28%	78.47 - 79.31%
Risk-free interest rate	4.35 - 4.65%	3.47 - 3.98%	3.88 - 4.65%	3.47 - 3.98%
Dividend yield	–%	–%	–%	–%

Summary of Restricted Stock Units Activity

A summary of the Company’s RSU activity for the six months ended June 30, 2024 is as follows:

	Unvested Restricted Stock Units
(in thousands, except share and per share data)	Number of Shares			Weighted- Average Grant Date Fair Value		Aggregate Fair Value
Balance—December 31, 2023		1,253,826		$	8.99	$	2,633
RSUs granted		—			—
RSUs vested		(280,595	)		12.48		394
RSUs forfeited		(201,325	)		10.25
Balance—June 30, 2024		771,906		$	7.39	$	903

Stock Based Compensation Expense by Award Type and Function

The following is a summary of stock-based compensation expense by award type (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Service-based stock options	$	1,237	$	1,505	$	2,452	$	2,848
Performance-based stock options		35		—		41		—
RSUs		1,324		1,757		2,732		3,880
ESPP		57		223		115		452
Total stock-based compensation expense	$	2,653	$	3,485	$	5,340	$	7,180

The following is a summary of stock-based compensation expense by function (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Cost of revenue	$	153	$	436	$	307	$	926
Research and development		1,046		1,241		1,993		2,486
Selling, general and administrative		1,454		1,808		3,040		3,768
Total stock-based compensation expense	$	2,653	$	3,485	$	5,340	$	7,180

2019 Employee Stock Purchase Plan

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Weighted-average Assumptions Used in Determination of Fair Value of Stock Options

During the three and six months ended June 30, 2024 and 2023, 395,552 and 468,643 shares of common stock were purchased under the Employee Stock Purchase Plan ("ESPP"). The fair value of stock purchase rights granted under the ESPP was estimated using the following assumptions:

	Three and Six Months Ended June 30,
	2024			2023
Expected term (in years)		0.50			0.50
Volatility		61.35	%		84.88	%
Risk-free interest rate		5.43	%		5.14	%
Dividend yield	–%			–%
Grant-date fair value per share	$	0.51		$	0.91

2019 Employee Stock Purchase Plan | Performance-Based Stock Option

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Stock Option Activity

A summary of the Company's performance-based stock option activity for the six months ended June 30, 2024 is as follows:

	Outstanding Performance-Based Options
(in thousands, except share and per share data)	Number of Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance—December 31, 2023		—	$	—		—	$	—
Options granted		271,500		1.61
Balance—June 30, 2024		271,500	$	1.61		9.71	$	—
Options vested and exercisable as of June 30, 2024		—