Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

The following table summarizes stock option activity for the year ended December 31, 2020 (in thousands, except share and per share amounts):


	Options Outstanding		Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (years)		Aggregate Intrinsic Value

Balance as of December 31, 2019		497,441,159	$	4.10		5.81	$	975,798
Options granted (1)		397,885,337		7.43
Options exercised		(120,617,527)		2.48
Options canceled and forfeited (1)		(238,942,466)		5.95

Balance as of December 31, 2020		535,766,503	$	6.12		7.99	$	9,340,245

Options vested and exercisable as of December 31, 2020		304,428,660	$	3.67		5.84	$	6,051,074

(1)

Includes options that were canceled and

re-granted

as part of the option repricing modification, as further discussed below.

Summary of Fair Value Assumptions of Stock-based Option Awards

The estimated grant-date fair value of all the Company’s stock-based option awards was calculated using the Black-Scholes option-pricing model, based on the following assumptions:


	Years Ended December 31,
	2020 (1)		2019 (1)		2018 (1)

Fair value of common stock	$	7.60	$	6.03	$	6.03
Expected volatility		71.00%		65.00%		65.00%
Expected term (in years)		12.04		6.36		6.50
Expected dividend yield		—%		—%		—%
Risk-free interest rate		0.64%		1.65%		2.97%

(1)

Excludes the impact of repricing of stock options modified during the years ended December 31, 2020, 2019, and 2018. See the “Stock Option Modification” subsection below for further information.

Summary of RSU Activity

The following table summarizes the RSU activity for the year ended December 31, 2020:


	RSUs Outstanding		Weighted Average Grant Date Fair Value per Share

Unvested and outstanding as of December 31, 2019		179,494,619	$	6.03
RSUs granted		98,667,215		8.15
RSUs vested		(82,429,575)		6.45
RSUs canceled		(10,862,021)		6.06

Unvested and outstanding at December 31, 2020		184,870,238	$	6.97

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense was as follows (in thousands):


	Years Ended December 31,
	2020		2019		2018
Cost of revenue	$	139,627	$	27,904	$	19,629
Sales and marketing		398,205		79,215		93,510
Research and development		357,063		67,933		72,039
General and administrative		375,807		66,918		63,325

Total stock-based compensation expense	$	1,270,702	$	241,970	$	248,503