Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2023

Nonvested Restricted Stock Shares Activity

RSU activity for the three months ended March 31, 2023 was as follows:

	Shares			Weighted- Average Grant-Date Fair Value
Unvested at December 31, 2022		456,766		$	26.70
Granted		374,458			41.59
Vested and released		(45,206	)		24.58
Cancelled		(12,358	)		33.67
Unvested at March 31, 2023		773,660		$	33.92

Summary of Activity under Employee Stock Purchase Plan

Activity under our 2020 ESPP was as follows:

	Shares
Balance - December 31, 2021		1,070,704
Additional shares authorized		530,319
Shares purchased		(61,709	)
Balance - December 31, 2022		1,539,314
Additional shares authorized		794,706
Shares purchased		—
Balance - March 31, 2023		2,334,020

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 three months ended March 31, 2023 and 2022 using the following weighted-average assumptions:

	Three Months Ended March 31,
	2023	2022
Fair Value Assumptions
Expected volatility	73.6% - 74.0%	78.1% - 78.9%
Expected dividend yield	0%	0%
Expected term (in years)	5.3 - 5.4	5.4
Risk-free interest rate	3.7% - 4.3%	1.6% - 2.4%

2020 Plan and 2014 Plan

Summary of Activity Under Stock Option Plans

Stock options and RSUs 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 Options and Restricted Stock Units Activity	Options and Restricted Stock Units Available for Grant				Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances — December 31, 2022		4,679,598				7,715,494		$	18.70
Additional shares authorized		3,973,533
Options granted		(1,574,642	)			1,574,642		$	41.84
Options exercised		1,080		(1)		(102,044	)	$	5.40
Options forfeited		41,058				(41,058	)	$	31.95
Restricted stock units granted		(374,458	)
Restricted stock units withheld		17,525
Restricted stock units forfeited		12,358
Balances — March 31, 2023		6,776,052				9,147,034		$	22.77		8.32	$	146,986
Vested and expected to vest — March 31, 2023						9,147,034		$	22.77		8.32	$	146,986
Exercisable at March 31, 2023						3,242,028		$	10.88		6.85	$	86,670

(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 three months ended March 31, 2023 and 2022 using the following weighted-average assumptions:

	Three Months Ended March 31,
	2023	2022
Fair Value Assumptions
Expected volatility	86.4% - 99.7%	86.7% - 97.5%
Expected dividend yield	0%	0%
Expected term (in years)	0.5 - 2.0	0.5 - 2.0
Risk-free interest rate	4.5% - 4.7%	0.1% - 0.5%

2014 Plan, 2020 Plan and 2020 ESPP

Summary of Stock-based Compensation Expense

We recorded total stock-based compensation expense for the three months ended March 31, 2023 and 2022 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the condensed statements of operations and allocated the amounts as follows:

	Three Months Ended March 31,
	2023		2022
	(in thousands)
Research and development	$	4,527	$	1,775
General and administrative		5,121		2,324
Total	$	9,648	$	4,099