Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense recognized for the years ended December 31, 2021, 2020 and 2019, as follows:

	2021		2020		2019
Research and development	$	7,416	$	6,110	$	181
Sales and marketing	8,770		4,505		111
General and administrative	44,145		13,142		945
Total stock-based compensation expense	$	60,331	$	23,757	$	1,237

Summary of Stock Option and RSU Activity

Stock option and RSU activity during the year ended December 31, 2021 is as follows (in thousands, except for share, per share, and contractual term data):

		Options Outstanding						Restricted Stock Units
	Number of Shares Available for Issuance Under the Plan	Number of Shares Outstanding Under the Plan	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value		Number of Plan shares outstanding	Weighted-Average Grant Date Fair Value per share
Balance at December 31, 2020	35,500,603	38,404,493	$	5.89	8.27	$	542,074	341,256	$	17.68
Options and restricted stock units granted	(8,494,636)	64,839	12.58					8,424,462	14.32
Options exercised and restricted stock units released	—	(5,850,228)	0.66					(117,933)	17.40
Options and restricted stock units canceled	5,939,704	(4,892,016)	1.17					(1,047,688)	23.37
Balance at December 31, 2021	32,945,671	27,727,088	$	7.79	7.04	$	113,110	7,600,097	$	13.17
Exercisable at December 31, 2020		14,248,234	$	0.18	6.45	$	282,364
Exercisable at December 31, 2021		13,157,036	$	0.15	5.17	$	95,946
Unvested at December 31, 2020		24,156,259	$	9.25	9.34	$	259,710
Unvested at December 31, 2021		14,570,052	$	14.69	8.72	$	17,164

Summary of Stock Option Valuation Assumptions

The assumptions used to estimate the fair value of stock options granted and the resulting fair values for the year ended December 31, 2021, 2020 and 2019 were as follows:

	2021	2020	2019
Expected volatility	48.71%	45% – 50%	47.17% – 55.47%
Risk-free interest rate	0.02%	0.27% – 1.44%	1.57% – 2.64%
Expected term (in years)	0.25	4.14-6.25	5.00 – 6.86
Expected dividend yield	—	—	—
Weighted average estimated fair value of stock options granted during the year	$15.63	$5.06	$0.21