The following table summarizes the components of stock-based compensation expense in the condensed consolidated statements of operations (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021

Cost of revenue	$	4,767	$	3,804	$	8,627	$	6,803
Research and development	13,213		5,291		20,295		10,199
Sales and marketing	4,805		4,010		9,580		8,095
General and administrative	9,814		6,028		20,405		11,246
	$	32,599	$	19,133	$	58,907	$	36,343

The following table summarizes the stock option activity under our stock plans during the reporting period:


	Outstanding Options
	Number of Shares	Weighted Average Exercise Price		Remaining Contractual Life (Years)	Aggregate Intrinsic Value

					(in thousands)












Balances at December 31, 2021	10,737,295	$	21.23	5.2	$	60,304

Exercised	(243,062)	5.33
Forfeited	(29,134)	8.27
Expired	(226,635)	30.41
Balances at June 30, 2022	10,238,464	21.44		4.7	32,857
Vested and expected to vest at June 30, 2022	10,206,941	21.49		4.7	32,567
Exercisable at June 30, 2022	9,093,852	$	22.86	4.4	24,841

Stock Options - During the three and six months ended June 30, 2022, we recognized $3.4 million and $5.5 million of stock-based compensation expense for stock options, respectively. During the three and six months ended June 30, 2021, we recognized $3.4 million and $7.3 million of stock-based compensation expense for stock options, respectively. We did not grant options in the three and six months ended June 30, 2022 and 2021.

As of June 30, 2022 and December 31, 2021, we had unrecognized compensation expense related to unvested stock options of $2.0 million and $6.2 million, respectively. This expense is expected to be recognized over the remaining weighted-average period of 0.4 years and 0.9 years, respectively. Cash received from stock options exercised totaled $1.3 million and $60.9 million for the six months ended June 30, 2022 and 2021, respectively.


	Number of Awards Outstanding	Weighted Average Grant Date Fair Value













Unvested Balance at December 31, 2021	8,367,664	$	20.52
Granted	4,440,721	19.12
Vested	(1,789,639)	17.53
Forfeited	(427,022)	22.70
Unvested Balance at June 30, 2022	10,591,724	19.70

Stock Awards - The estimated fair value of restricted stock units ("RSUs") and performance stock units ("PSUs") is based on the fair value of our Class A common stock on the date of grant. During the three and six months ended June 30, 2022, we recognized $25.0 million and $46.0 million of stock-based compensation expense for stock awards, respectively. During the three and six months ended June 30, 2021, we recognized $14.1 million and $24.8 million of stock-based compensation expense for stock awards, respectively.

As of June 30, 2022 and December 31, 2021, we had $172.3 million and $114.9 million of unrecognized stock-based compensation expense related to unvested stock awards, expected to be recognized over a weighted average period of 2.2 years and 2.3 years, respectively.

The following table presents the stock activity for the six months ended June 30, 2022 and the total number of shares available for grant under our stock plans as of June 30, 2022:


						Plan Shares Available for Grant
Balances at December 31, 2021						24,146,784
Added to plan						8,384,460
Granted						(4,507,452)

Cancelled/Forfeited						602,506
Expired						(211,521)
Balances at June 30, 2022						28,414,777

During the six months ended June 30, 2022 and 2021, we recognized $6.9 million and $2.2 million of stock-based compensation expense for the 2018 Employee Stock Purchase Plan, respectively. We issued 420,689 and 977,508 shares in the six months ended June 30, 2022 and 2021, respectively. During the six months ended June 30, 2022 and 2021, we added an additional 2,055,792 shares and 1,902,572 shares, respectively. There were 4,179,771 shares and 3,512,465 shares available for issuance as of June 30, 2022 and 2021, respectively.

As of June 30, 2022 and December 31, 2021, we had $6.4 million and $9.8 million of unrecognized stock-based compensation expense, expected to be recognized over a weighted average period of 1.2 years and 0.5 years, respectively.