We maintain three share-based employee compensation plans: the 2017 Equity Incentive Plan (“2017 Plan”), the 2014 Equity Incentive Plan (“2014 Plan”), and the 2012 Equity Incentive Plan (“2012 Plan”, and collectively with the 2017 Plan and the 2014 Plan, the “Stock Plans”). In January 2017, our board of directors adopted the 2017 Plan, and in February 2017 our stockholders approved the 2017 Plan, effective on March 1, 2017, which serves as the successor to the 2014 Plan and 2012 Plan and provides for the grant of incentive stock options to employees, including employees of any parent or subsidiary, and for the grant of nonstatutory stock options, stock appreciation rights, RSAs, RSUs, performance stock awards, performance cash awards, and other forms of stock awards to employees, directors, and consultants, including employees and consultants of our affiliates.

The following table summarizes the RSU and RSA activity during the nine months ended September 30, 2021:

	Class A Outstanding			Weighted- Average Grant Date Fair Value
	(in thousands, except per share data)
Unvested at December 31, 2020		131,172		$	15.10
Granted		18,168		$	59.13
Vested		(45,486	)	$	15.64
Forfeited		(7,980	)	$	15.04
Unvested at September 30, 2021		95,874		$	23.19

All RSUs and RSAs granted after December 31, 2016 vest on the satisfaction of only a service-based condition (“Post-2017 Awards”). Total unrecognized compensation cost related to Post-2017 Awards was $2.0 billion as of September 30, 2021 and is expected to be recognized over a weighted-average period of 2.3 years. The service condition for Post-2017 Awards granted prior to February 2018 is generally satisfied over four years, 10% after the first year of service, 20% over the second year, 30% over the third year, and 40% over the fourth year. In limited instances, we have issued Post-2017 RSUs with vesting periods in excess of four years. The service condition for Post-2017 Awards granted after February 2018 is generally satisfied in equal monthly or quarterly installments over one to four years.

The following table summarizes the stock option award activity under the Stock Plans during the nine months ended September 30, 2021:

	Class A Number of Shares			Class B Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value⁽¹⁾
	(in thousands, except per share data)
Outstanding at December 31, 2020		4,828			796		$	10.37		5.20	$	223,230
Granted		48			—		$	49.63		—	$	—
Exercised		(891	)		(66	)	$	12.30		—	$	—
Forfeited		(7	)		—		$	13.53		—	$	—
Outstanding at September 30, 2021		3,978			730		$	10.38		4.41	$	298,934

Total unrecognized compensation cost related to unvested stock options was $4.9 million as of September 30, 2021 and is expected to be recognized over a weighted-average period of 1.0 year.

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
	(in thousands)
Cost of revenue	$	9,132	$	2,623	$	14,635	$	6,471
Research and development		198,893		132,003		537,177		377,836
Sales and marketing		51,675		27,393		118,250		79,306
General and administrative		41,198		30,061		124,509		86,687
Total	$	300,898	$	192,080	$	794,571	$	550,300