Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2022

Nonvested Restricted Stock Shares Activity

RSU activity for the year ended December 31, 2022 was as follows:

	Shares			Weighted- Average Grant-Date Fair Value
Unvested at December 31, 2021		—		$	—
Granted		581,047			26.25
Vested and released		(79,229	)		24.79
Cancelled		(45,052	)		24.32
Unvested at December 31, 2022		456,766		$	26.70

Summary of Activity under Employee Stock Purchase Plan

Activity under our 2020 ESPP was as follows:

	Shares
Balance - December 31, 2019		—
Shares authorized		650,000
Shares purchased		(27,465	)
Balance - December 31, 2020		622,535
Additional shares authorized		510,715
Shares purchased		(62,546	)
Balance - December 31, 2021		1,070,704
Additional shares authorized		530,319
Shares purchased		(61,709	)
Balance - December 31, 2022		1,539,314

Summary of Estimated Fair Value of Employee Stock Options

We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the years ended December 31, 2022, 2021 and 2020 using the following weighted-average assumptions:

	Year Ended December 31,
	2022	2021	2020
Fair Value Assumptions
Expected volatility	78.1% - 85.1%	81.0% - 84.1%	81.2% - 94.1%
Expected dividend yield	0%	0%	0%
Expected term (in years)	5.3 - 5.5	5.3 - 5.5	5.6 - 6.1
Risk-free interest rate	1.6% - 4.4%	0.5% - 1.3%	0.3% - 1.4%

2020 Plan and 2014 Plan

Summary of Activity Under Stock Option Plans

Stock option activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 36,710 shares granted outside of the 2020 Plan and 2014 Plan, was as follows:

					Options Outstanding
Stock Option and Restricted Stock Units Activity	Options and RSUs Available for Grant				Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances — December 31, 2020		4,651,149				5,121,549		$	4.99
Additional shares authorized		2,553,579				—
Options granted		(1,616,021	)			1,616,021		$	21.83
Options exercised		—				(926,514	)	$	3.25
Options forfeited		516,049				(516,049	)	$	16.70
Balances — December 31, 2021		6,104,756				5,295,007		$	9.30
Additional shares authorized		2,651,598				—
Options granted		(3,850,981	)			3,850,981		$	27.67
Options exercised		385		(1)		(1,153,285	)	$	4.25
Options forfeited		277,209				(277,209	)	$	23.54
Restricted Stock Units granted		(581,047	)
Restricted Stock Units withheld		32,626
Restricted Stock Units forfeited		45,052
Balances — December 31, 2022		4,679,598				7,715,494		$	18.70		8.20	$	225,667
Vested and expected to vest — December 31, 2022						7,715,494		$	18.70		8.20	$	225,667
Exercisable at December 31, 2022						2,921,091		$	9.41		6.81	$	112,585

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(1)Net exercise - shares returned to the Plan.

2020 Employee Stock Purchase Plan

Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan

We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the years ended December 31, 2022, 2021 and 2020 using the following weighted-average assumptions:

	Year Ended December 31,
	2022	2021	2020
Fair Value Assumptions
Expected volatility	78.8% - 99.7%	79.6% - 126.3%	105.8% - 158.2%
Expected dividend yield	0%	0%	0%
Expected term (in years)	0.5 - 2.0	0.5 - 2.0	0.4 - 2.0
Risk-free interest rate	0.1% - 4.7%	0.0% - 0.5%	0.1% - 0.2%

2014 Plan, 2020 Plan and 2020 ESPP

Summary of Stock-based Compensation Expense

We recorded total stock-based compensation expense for the years ended December 31, 2022, 2021 and 2020 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the statements of operations and allocated the amounts as follows:

	Year Ended December 31,
	2022		2021		2020
	(In thousands)
Research and development	$	9,899	$	3,954	$	1,861
General and administrative		13,751		6,775		3,573
Total	$	23,650	$	10,729	$	5,434