The board of directors was authorized to grant stock-based awards under the 2015 Equity Incentive Plan (the “2015 Plan”). Following the effectiveness of the 2020 Plan (as defined below), the 2015 Plan was terminated. However, any outstanding awards granted under the 2015 Plan will remain outstanding, subject to the terms of the 2015 Plan and applicable award agreement. Shares of Class A common stock subject to awards granted under the 2015 Plan that expire unexercised or are cancelled, terminated or forfeited in any manner without issuance of shares thereunder following the effective date of the 2020 Plan, have or will become available for issuance under the 2020 Plan in accordance with its terms.

In connection with the Company’s IPO in 2020, its board of directors adopted, and its stockholders approved, the 2020 Incentive Award Plan (the “2020 Plan”), which provides for the grant of stock options, including incentive stock options, or ISOs, and nonqualified stock options, or NSOs, restricted stock, dividend equivalents, RSUs, stock appreciation rights (SARs), and other stock or cash based awards to its employees, consultants and directors, and employees, consultants and directors of its subsidiaries. The board of directors or its Compensation Committee is authorized to grant stock-based awards under the 2020 Plan.

An aggregate of 60.7 million shares of Class A and Class B common stock initially were available for issuance under awards granted pursuant to the 2020 Plan, which shares may be authorized but unissued shares, treasury shares or shares purchased in the open market. Shares may be issued under the 2020 Plan as either Class A or Class B common stock. Notwithstanding anything to the contrary in the 2020 Plan, no more than 300.0 million shares of common stock (either Class A or Class B common stock) may be issued pursuant to the exercise of incentive stock options under the 2020 Plan.

The number of shares available for issuance under the 2020 Plan will be increased by an annual increase on the first day of each calendar year beginning January 1, 2021 and ending on and including January 1, 2030, equal to the lesser of (A) 5% of the aggregate number of shares of Class A and Class B common stock outstanding on the final day of the immediately preceding calendar year and (B) such smaller number of shares as is determined by the Company’s board of directors.

At December 31, 2020, 34.4 million shares were available for issuance under the 2020 Plan.

In connection with the Company’s IPO in 2020, its board of directors adopted, and its stockholders approved, the 2020 Employee Stock Purchase Plan (ESPP). A total of 9.0 million shares of Class A common stock were initially reserved for issuance under the ESPP. In addition, the number of shares available for issuance under the ESPP will be annually increased on January 1 of each calendar year beginning in 2021 and ending in 2030, by an amount equal to the lesser of: (i) 1% of the aggregate number of shares of Class A and Class B common stock outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares as is determined by the Company’s board of directors. In no event will more than 100.0 million shares of Class A common stock be available for issuance under the ESPP.

The ESPP allows eligible employees to purchase common stock of the Company, through payroll deductions, at 85% of the lower of the fair market value of Class A common stock on the first trading day of the offering period or on the applicable purchase date, which will be the final trading day of the applicable purchase period. The ESPP is intended to qualify as an employee stock purchase plan under the Internal Revenue Service (“IRS”) Code Section 423. Eligible employees may contribute up to a certain percentage set by the plan administrator of their eligible earnings toward the purchase of the stock (subject to certain IRS limitations). At December 31, 2020, 9.0 million shares were available for issuance under the ESPP.

There were no employee stock purchase offerings during 2020 and accordingly no eligible employees were enrolled in the ESPP during 2020.

Stock options granted generally vest 25% of the total award on the first anniversary of the vesting commencement date, and thereafter ratably monthly over the remaining three-year period. Stock options generally have a ten-year term. Stock options granted under the 2015 Plan and 2020 Plan do not include any forfeitable or non-forfeitable dividend equivalent rights.

A summary of the stock option activity is as follows, in thousands, except per share amounts and term information:

						Weighted
				Weighted		Average
				Average		Remaining	Aggregate
				Exercise		Contractual	Intrinsic
	Shares			Price		Term	Value
Outstanding at December 31, 2019		16,850		$	3.82
Granted		10,019			8.78
Exercised		(3,769	)		2.87
Expired / Cancelled / Forfeited		(1,572	)		4.93
Outstanding at December 31, 2020		21,528		$	6.22	8.1 years	$	734,604
Exercisable at December 31, 2020		9,012		$	3.73	7.1 years	$	329,945

The weighted-average grant date fair value per share of stock options granted for the years ended December 31, 2020, 2019 and 2018 was $4.23, $1.27 and $1.17, respectively. The aggregate intrinsic value of options exercised for the years ended December 31, 2020, 2019 and 2018 was $112.7 million, $11.1 million and $11.2 million, respectively. The fair value of stock options that vested during the years ended December 31, 2020, 2019 and 2018 was $10.2 million, $2.5 million and $1.6 million, respectively.

All stock options outstanding at December 31, 2020 are options to purchase shares of Class A Common Stock. The fair value of option awards issued with service and performance vesting conditions are estimated on the grant date using the Black-Scholes option pricing model. The following table summarizes the assumptions used:

	Year Ended December 31,
	2020		2019		2018
Risk-free interest rate	0.4% - 1.4%		1.4% - 2.4%		2.7% - 2.9%
Expected term	5.3 - 6.3 years		5.6 - 6.3 years		5.7 - 6.1 years
Expected stock price volatility	50% - 62%		50%		60%
Dividend yield		—		—		—
Fair value of common stock per share	$5.94 - $33.00		$2.75 - $5.88		$1.05 - $2.75

For the years ended December 31, 2020, 2019 and 2018, the stock-based compensation expense related to stock options was $13.0 million, $2.5 million and $1.8 million, respectively. At December 31, 2020, there was $36.8 million of total unrecognized stock-based compensation cost related to stock options, excluding stock options which contain performance and market conditions described below, which is expected to be recognized over a weighted-average remaining service period of 3.0 years.

In June 2020, the Company granted stock options to purchase 0.6 million shares of common stock at an exercise price of $6.84 per share that vest upon continued service and the achievement of both performance and market conditions. For stock options to purchase 0.4 million shares of common stock, the service condition is satisfied monthly over a 4-year period and for stock options to purchase 0.2 million shares of common stock the service condition is satisfied on January 1, 2022. The performance condition is satisfied upon the closing of the Company’s IPO. The market condition is satisfied upon the Company’s common stock achieving a per share price threshold in the IPO, an average trading price of the Company’s stock for a period subsequent to the IPO, or a per share price in a change in control transaction. Both the market and performance conditions were met upon the closing of the Company’s IPO. The Company estimated the grant date fair value of these awards to be $1.4 million using a Monte Carlo simulation model. The Company recognized $0.6 million of stock-based compensation expense in the year ended December 31, 2020 related to these stock options.

In June 2020, the Company modified the terms of a grant to purchase 0.4 million shares of common stock. The original award that would otherwise have been cancelled upon the employee’s departure from the Company was modified to permit the former employee to only exercise the award within 30 days after the completion of a performance condition, which are the Company completing its IPO or a change in control of the Company or a declaration of dividend payment, as defined. The fair value of this stock option of $2.4 million on the modification date was recognized as stock-based compensation expense on the effective date of the Company’s IPO.

A summary of the Restricted Stock Awards and Restricted Stock Unit 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, 2019		1,879			—			—			$	3.88
Granted		—			2,800			24,633				23.56
Vested		(470	)		(8	)		(16,935	)	⁽¹⁾		19.26
Forfeited		—			(2	)		—				49.05
Nonvested restricted stock awards or restricted stock units at December 31, 2020		1,409			2,790			7,698			$	26.74
⁽¹⁾ Includes 15,691 of restricted stock units vested but not yet settled related to the Performance-Vesting Founders Awards.

For the year ended December 31, 2020, the fair value of RSAs and RSUs that vested was $335.4 million. The fair value of RSAs that vested during 2019 and 2018 was not material. There were no RSUs granted or outstanding during the years ended December 31, 2019 and 2018.

The weighted-average fair value per share of RSAs granted for the year ended December 31, 2019 was $3.88. For the years ended December 31, 2020 and 2019, total stock-based compensation expense related to RSAs was $1.8 million and $1.3 million, respectively. At December 31, 2020, there was $4.2 million of total unrecognized stock-based compensation cost related to these RSAs which is expected to be recognized over the remaining service period of 2.3 years. There were no RSAs granted during the year ended December 31, 2018.

For the year ended December 31, 2020, the Company granted RSUs for Class A Common Stock. Substantially all of the RSUs granted vest upon continued service over a four-year period. For the year ended December 31, 2020, total stock-based compensation expense related to RSUs was $9.5 million. At December 31, 2020, there was $109.0 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 3.7 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, 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 in equal quarterly installments over four years, subject to continued employment through the applicable vesting date (the “Time-Vesting Founders Awards”). Any Performance-Vesting Founders Awards that vest will be settled in shares of common stock on the third anniversary of the applicable vesting date or, if earlier, upon a qualifying change in control event or to satisfy tax withholding requirements. The Performance-Vesting Founders Awards and Time-Vesting Founders Awards are subject to certain vesting acceleration terms. The grant date fair value of these awards was $533.3 million. The Company used a Monte Carlo simulation model to calculate the grant date fair value of the Performance-Vesting Founders Awards and the derived service period. The Monte Carlo simulation model incorporates the likelihood of achieving the market condition and requires the input of assumptions including the estimated fair value of common stock, expected volatility, expected term, risk-free rate and dividend yield. The primary inputs used in the Monte Carlo simulation model were volatility of 55% and estimated cost of equity of 11%. The Company then applied a 20% DLOM to the value of the RSUs as the issuance of the shares for these awards is deferred by three-years from the applicable vesting date, or earlier, upon a qualifying change in control or to satisfy tax withholding requirements. The Company utilized the Finnerty Model to calculate the DLOM using inputs, including length of holding period, volatility and dividend yield, with volatility considered as a significant Level 3 input in the fair value hierarchy. 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, resulting in recognition of approximately $232.1 million of stock-based compensation expense during the fourth quarter of 2020. The grant date fair value of the Time-Vesting Founders Awards was estimated based on the fair value of the Company's common stock on the date of grant.

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 three years from the vesting date or, if earlier, a change in control event, as defined in the RSU agreements governing the Founders Awards.

During the year ended December 31, 2020, the Company has recognized a cumulative $373.0 million of stock-based compensation expense, with $53.2 million related to the Time-Vesting Founders Awards and $319.8 million related to the Performance-Vesting Founders Awards. At December 31, 2020, there was $160.3 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 2.1 years.

The Company recognized excess tax benefits of $21.7 million, $0.9 million and $1.3 million associated with equity award exercises and vesting in its income tax benefit (expense) for the years ended December 31, 2020, 2019 and 2018, respectively.

To meet the related tax withholding requirements for the year ended December 31, 2020, the Company withheld 1.8 million shares of common stock, inclusive of the settlement of 0.7 million RSUs related to the Performance-Vesting Founders Awards, which were returned to the shares reserved for future issuance under the Company’s 2020 Plan. The Company anticipates expending substantial funds to satisfy tax withholding and remittance obligations as the equity awards vest over time.

In connection with the dividend payments made to stockholders in May 2018 and October 2018, as further described in “Note 14. Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit),” the Company paid vested option holders cash bonuses totaling $38.8 million which are included in the following components of expenses on the accompanying consolidated statement of operations for the year ended December 31, 2018 as follows:

The payment of cash bonuses to vested option holders was not required under terms of the options or the 2015 Plan, and did not result in a modification of the stock options.