A summary of the stock option activity is as follows:


						Weighted
				Weighted		Average
				Average		Remaining	Aggregate
				Exercise		Contractual	Intrinsic
(in thousands, except per share amounts and term information)	Shares			Price		Term	Value
Outstanding at December 31, 2020		21,528		$	6.22
Granted		—			—
Exercised		(513	)		5.23
Expired / Cancelled / Forfeited		(253	)		6.07
Outstanding at March 31, 2021		20,762		$	6.24	7.9 years	$	680,528
Granted		—			—
Exercised		(2,609	)		5.09
Expired / Cancelled / Forfeited		(222	)		7.71
Outstanding at June 30, 2021		17,931		$	6.39	7.7 years	$	531,079
Exercisable at June 30, 2021		8,756		$	4.36	6.8 years	$	277,143

There were no stock options granted during the three and six months ended June 30, 2021. The weighted-average grant date fair value per share of stock options granted for the three and six months ended June 30, 2020 was $3.17 and $3.04, respectively. The aggregate intrinsic value of options exercised for the three months ended June 30, 2021 and 2020 was $79.9 million and $1.0 million, respectively. The aggregate intrinsic value of options exercised for the six months ended June 30, 2021 and 2020 was $98.6 million and $2.4 million, respectively.

All options outstanding at June 30, 2021 are options to purchase shares of Class A common stock. The fair value of option awards issued with service or service and performance vesting conditions are estimated on the grant date using the Black-Scholes option pricing model. The Company does not have material stock options issued with market vesting conditions.

For the three months ended June 30, 2021 and 2020, the stock-based compensation expense related to stock options was $3.9 million and $1.7 million, respectively. For the six months ended June 30, 2021 and 2020, the stock-based compensation expense related to stock options was $8.1 million and $3.4 million, respectively. At June 30, 2021, there was $26.5 million of total unrecognized stock-based compensation cost related to stock options, which is expected to be recognized over a weighted average remaining service period of 2.5 years.

A summary of the Restricted Stock Awards (“RSAs”) and Restricted Stock Unit (“RSUs”) activity is as follows:


	Restricted			Restricted Stock Units for Class A			Restricted Stock Units for Class B			Weighted Average
	Stock			Common			Common			Grant Date
(in thousands, except per share amounts)	Awards			Stock			Stock			Fair Value
Nonvested restricted stock awards or restricted stock units at December 31, 2020		1,409			2,790			7,698		$	26.74
Granted		—			647			—			44.12
Vested		—			(95	)		(513	)		29.12
Forfeited		—			(17	)		—			42.31
Nonvested restricted stock awards or restricted stock units at March 31, 2021		1,409			3,325			7,185		$	28.05
Granted		—			618			—			37.86
Vested		(470	)		(118	)		(513	)		18.68
Forfeited		—			(67	)		—			36.61
Nonvested restricted stock awards or restricted stock units at June 30, 2021		939			3,758			6,672		$	29.44

There were no RSUs granted or outstanding during the three and six months ended June 30, 2020.

For the three months ended June 30, 2021 and 2020, total stock-based compensation expense related to RSAs was $0.5 million and $0.4 million, respectively. For the six months ended June 30, 2021 and 2020, total stock-based compensation expense related to RSAs was $1.0 million and $0.9 million, respectively. At June 30, 2021, there was $3.2 million of total unrecognized stock-based compensation cost related to these RSAs which is expected to be recognized over the remaining service period of 1.8 years. There were no RSAs granted subsequent to December 31, 2019.

For the three and six months ended June 30, 2021, total stock-based compensation expense related to RSUs for Class A common stock was $12.3 million and $24.1 million, respectively. At June 30, 2021, there was $131.7 million of total unrecognized stock-based compensation cost related to these RSUs which is expected to be recognized over the weighted average remaining service period of 3.4 years.

On September 11, 2020, the board of directors granted RSUs covering an aggregate of 24,633,066 shares of Class B common stock to the Company’s Co-Chief Executive Officers (the “Founders Awards”), subject to the completion of the Company’s initial public offering. Each of the Co-Chief Executive Officers received (i) 8,211,022 RSUs that vest based on the achievement of stock price goals ranging from $6.07 per share to $51.28 per share, subject to continued employment through the applicable vesting date (the “Performance-Vesting Founders Awards”) and (ii) 4,105,511 RSUs that vest and settle in equal quarterly installments over four years, subject to continued employment through the applicable vesting date (the “Time-Vesting Founders Awards”). The grant date fair value of these awards was $533.3 million. The Performance-Vesting Founders Awards vested during the fourth quarter of 2020 and will be settled in shares of common stock in October 2023 or, if earlier, upon a qualifying change in control event or to satisfy tax withholding requirements. The Time-Vesting Founders Awards are subject to vesting acceleration terms upon a qualifying change in control. All the stock price goals with respect to the Performance-Vesting Founders Awards were achieved as of October 22, 2020. As a result, all 16,422,044 Performance-Vesting Founders Awards vested during the year ended December 31, 2020. As of June 30, 2021, the Company has recognized a cumulative $427.0 million of stock-based compensation expense related to the Founders Awards, of which $107.2 million related to the Time-Vesting Founders Awards and $319.8 million related to the Performance-Vesting Founders Awards. During the three and six months ended June 30, 2021, the Company recognized stock-based compensation expense related to the Time-Vesting Founders Awards of $24.0 million and $54.0 million, respectively. At June 30, 2021, there was $106.3 million of total unrecognized stock-based compensation cost related to the Time-Vesting Founders Awards, which is expected to be recognized over the weighted average remaining service period of 1.9 years. The Company expects to recognize a total of $36.9 million in stock-based compensation expense related to the Time-Vesting Founders Awards in the second half of 2021.

As the Performance-Vesting Founders Awards vested in October 2020, the Company settled 0.7 million RSUs during the fourth quarter of 2020, sufficient to satisfy FICA tax withholding obligations due in the year of vesting. The remaining 15.7 million Performance-Vesting Founders Awards shares will not be issued until October 2023 or, if earlier, a change in control event, as defined in the RSU agreements governing the Founders Awards.