Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Employee and Non-Employee Stock-Based Compensation Expense

The following table summarizes employee and non-employee stock-based compensation expense for the years ended December 31, 2021, 2020, and 2019 and the allocation within the statements of operations and comprehensive loss (in thousands):

	2021		2020		2019
General and administrative expense	$	14,792	$	7,441	$	1,378
Research and development expense		15,061		7,029		678
Total stock-based compensation	$	29,853	$	14,470	$	2,056

Service Based Stock Options

Summary of Stock Options Activity

Activity for service-based stock options under the 2019 Plan is as follows:

	Number of Options and Unvested Shares			Weighted Average Exercise Price		Weighted average remaining contractual life (years)		Aggregate intrinsic value
								(In thousands)
Balance at December 31, 2018		1,885,504		$	1.57	9.07		$	1,253
Options granted		932,639			15.87	—		—
Options exercised		(194,279	)		0.51	—		—
Options cancelled / forfeited		(229,930	)		21.09	—		—
Balance at December 31, 2019		2,393,934		$	5.35		8.62	$	121,593
Options granted		2,798,645			42.95	—		—
Options exercised		(173,809	)		7.38	—		—
Options cancelled / forfeited		(228,443	)		42.56	—		—
Balance at December 31, 2020		4,790,327		$	25.47		8.69	$	49,723
Options granted		1,436,116			35.20	—		—
Options exercised		(531,190	)		12.82	—		—
Options cancelled / forfeited		(123,960	)		47.09	—		—
Balance at December 31, 2021		5,571,293		$	28.70		8.26	$	15,687
Options vested and expected to vest to December 31, 2021		5,571,293			28.70		8.26		15,687
Options exercisable at December 31, 2021		2,232,953		$	19.91		7.29	$	11,984

Summary of Weighted Average Assumptions to Calculate the Fair Value of Stock-Based Compensation

The following weighted average assumptions were used to calculate the fair value of stock-based compensation for the years ended December 31, 2021, 2020, and 2019:

	2021			2020			2019
Expected volatility		87.56	%		86.69	%		80.19	%
Expected dividend yield		—	%		—	%		—	%
Expected term (in years)		6.23			6.23		6.25
Risk-free interest rate		1.15	%		0.80	%		1.90	%

Performance Stock Options

Summary of Stock Options Activity

The following table summarizes activity under the Company’s PSOs from the 2019 Plan and related information:

	Shares Subject to Outstanding PSOs		Weighted Average Exercise Price		Weighted average remaining contractual life (years)
Balance at December 31, 2020		675,000	$	29.60		9.94
Balance at December 31, 2021		675,000		29.60		8.94
Outstanding		675,000	$	29.60		8.94
Vested	—		—		—

Market Based Performance Stock Options

Summary of Weighted Average Assumptions to Calculate the Fair Value of Stock-Based Compensation

The Company estimated the grant date fair value of its market-based performance stock option awards granted during the year ended December 31, 2020 using a Monte Carlo Simulation method by applying the following assumptions:

Expected share price volatility	95.0	%
Contractual term, in years	10
Risk-free interest rate	0.90	%