Redeemable Convertible Preferred Stock and Stockholders’ Equity - Common Stock Outstanding (Details) - shares	Sep. 30, 2021	Aug. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock outstanding (in shares)	111,392,357		53,944,305
Employee stock options - outstanding (in shares)	5,713,130		7,795,040
Authorized (in shares)	1,050,000,000		150,000,000
Series A common stock
Class of Stock [Line Items]
Common stock outstanding (in shares)	93,353,364		52,895,029
Employee stock options - outstanding (in shares)	1,851,955		5,298,660
Shares of Series A common stock issuable upon conversion of all redeemable convertible preferred stock, exercise of all warrants for redeemable convertible preferred stock, outstanding Series B common stock, options, and RSUs	22,977,531		59,813,999
Total common stock – outstanding or issuable on exercise of options (in shares)	131,371,749		119,003,248
Authorized (in shares)	750,000,000	750,000,000	135,000,000
Common stock available for future issuance (in shares)	618,628,251		15,996,752
Series A common stock | Restricted stock units (RSUs)
Class of Stock [Line Items]
Restricted stock units - outstanding (in shares)	1,533,719		260,878
Series A common stock | Employee Stock
Class of Stock [Line Items]
Employee stock options - available (in shares)	11,655,180		734,682
Series B common stock
Class of Stock [Line Items]
Common stock outstanding (in shares)	18,038,993		1,049,276
Employee stock options - outstanding (in shares)	2,834,298		2,496,380
Shares of Series A common stock issuable upon conversion of all redeemable convertible preferred stock, exercise of all warrants for redeemable convertible preferred stock, outstanding Series B common stock, options, and RSUs	0		0
Total common stock – outstanding or issuable on exercise of options (in shares)	22,977,531		5,750,350
Authorized (in shares)	150,000,000	150,000,000	15,000,000
Common stock available for future issuance (in shares)	127,022,469		9,249,650
Series B common stock | Restricted stock units (RSUs)
Class of Stock [Line Items]
Restricted stock units - outstanding (in shares)	1,881,504		1,232,244
Series B common stock | Employee Stock
Class of Stock [Line Items]
Employee stock options - available (in shares)	222,736		972,450
Series C common stock
Class of Stock [Line Items]
Common stock outstanding (in shares)	0
Employee stock options - outstanding (in shares)	0
Shares of Series A common stock issuable upon conversion of all redeemable convertible preferred stock, exercise of all warrants for redeemable convertible preferred stock, outstanding Series B common stock, options, and RSUs	0
Total common stock – outstanding or issuable on exercise of options (in shares)	0
Authorized (in shares)	150,000,000	150,000,000
Common stock available for future issuance (in shares)	150,000,000
Series C common stock | Restricted stock units (RSUs)
Class of Stock [Line Items]
Restricted stock units - outstanding (in shares)	0
Series C common stock | Employee Stock
Class of Stock [Line Items]
Employee stock options - available (in shares)	0