Stock-based compensation expense recorded in the consolidated statements of operations was as follows (in thousands):

	Year Ended December 31,
	2021		2020		2019
Platform operations	$	15,913	$	8,794	$	5,350
Sales and marketing		50,671		29,726		20,769
Technology and development		57,791		36,672		26,553
General and administrative		213,038		36,583		28,086
Total	$	337,413	$	111,775	$	80,758

For the years ended December 31, 2021, 2020 and 2019, the Company recognized tax benefits on total stock-based compensation expense, which are reflected in the provision for income taxes in the consolidated statements of operations, of $104.4 million, $134.6 million, and $43.1 million, respectively. For the years ended December 31, 2021, 2020 and 2019, tax benefit realized related to restricted stock vested and stock options exercised during the period was $120.6 million, $151.0 million and $51.0 million, respectively.

The Company is authorized to issue stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based and cash-based awards under its 2016 Incentive Award Plan. As of December 31, 2021, 56.4 million shares remained available for grant under the Company’s 2016 Incentive Award Plan. The number of shares authorized for grant is subject to increase each year on January 1, equal to the lesser of (a) 4% of the common stock outstanding (on an as-converted basis) on the final day of the immediately preceding calendar year and (b) such smaller number of shares as determined by the board of directors. On January 1, 2022, the number of shares authorized for grant under the Company’s 2016 Incentive Award Plan was increased by 19.3 million shares in accordance with plan provisions.

Stock options granted under the Company’s stock incentive plans generally vest over four years, subject to the holder’s continued service through the vesting date and expire no later than 10 years from the date of grant.

	Shares Under Option (in thousands)			Weighted- Average Exercise Price		Weighted- Average Contractual Life (years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2020		26,481		$	10.73
Granted		1,212			74.85
Exercised		(7,361	)		8.36
Expired/forfeited		(1,348	)		19.18
Outstanding as of December 31, 2021		18,984		$	15.14		6.4	$	1,452,528
Exercisable as of December 31, 2021		13,008		$	8.69		5.7	$	1,079,090

The fair value of options on the date of grant was estimated based on the Black-Scholes option pricing model. The weighted- average assumptions used to value options granted to employees for the periods presented were as follows:

	Year Ended December 31,
	2021			2020			2019
Expected term (years)		6.0			6.0			6.0
Expected volatility		64.3	%		60.5	%		53.2	%
Risk-free interest rate		1.04	%		0.57	%		2.26	%
Estimated dividend yield		—	%		—	%		—	%

The weighted-average grant date fair value per share of stock options granted for the years ended December 31, 2021, 2020 and 2019 and were $43.57, $17.25 and $9.49, respectively. The total intrinsic value of options exercised during the years ended December 31, 2021, 2020 and 2019 were $538.0 million, $594.5 million and $222.0 million, respectively.

At December 31, 2021, the Company had unrecognized stock-based compensation relating to stock options of approximately $93.4 million, which is expected to be recognized over a weighted-average period of 1.8 years.

In October 2021, the Company granted a market-based performance award to the Company’s Chief Executive Officer (the “CEO Performance Option”) under the Company’s 2016 Incentive Award Plan. If specified target goals for the per share price of the Company’s Class A common stock (ranging from $90.00 to $340.00 per share) and certain other vesting conditions are satisfied, including the CEO’s continued service, the CEO may purchase up to a target amount of 16.0 million shares of Class A common stock, subject to adjustment as discussed in the following sentence, to be earned in eight equal tranches over a maximum term of 10 years. These target shares are subject to decrease or increase by up to 20% for each tranche based on the relative total shareholder return (“TSR”) of the Company’s Class A common stock as compared to the TSR of the Nasdaq-100 Index at each vesting tranche, for a maximum of 19.2 million shares. At December 31, 2021, the CEO Performance Option had 2.4 million exercisable options with an aggregate intrinsic value of $56.0 million, and a weighted-average contractual life of 9.8 years. At December 31, 2021, the CEO Performance Option had outstanding options of 19.2 million with an aggregate intrinsic value of $448.3 million and a weighted-average contractual life of 9.8 years. No options were exercised, forfeited or expired as of December 31, 2021. The CEO Performance Option has an exercise price of $68.29 per share and a grant-date fair value of approximately $819.0 million, which was estimated based on a Monte Carlo valuation model using the following assumptions:

The CEO Performance Option has a one-year holding period with respect to the sale or transfer of vested shares, with the exception that shares may be transferred during the holding period to cover withholding tax obligations in connection with such exercise and transfers to the CEO’s immediate family for estate planning purposes or in connection with charitable or philanthropic activities. Due to the holding period, the Company applies a discount to reflect the non-transferability of the shares. The stock-based compensation expense for the CEO Performance Option is expected to be expensed on a graded-vesting basis over a derived service period of approximately five years but may be accelerated if the vesting criteria are met prior to the estimated performance period.

On December 10, 2021, the expense related to the first tranche of the award was accelerated due to early stock price achievement. Stock-based compensation expense of $157.7 million for the CEO Performance Option, including the accelerated tranche, was recorded as a component of general and administrative expense in the fourth quarter of 2021. At December 31, 2021, the Company had unrecognized stock-based compensation relating to the CEO Performance Option of $661.3 million which, assuming no acceleration of vesting, is expected to be recognized over a weighted-average period of 3.0 years.

Restricted stock awards generally vest over four years, subject to the holder’s continued service through the vesting date.

	Shares (in thousands)			Weighted- Average Grant Date Fair Value Per Share
Unvested as of December 31, 2020		5,698		$	26.10
Granted		2,818			77.41
Vested		(2,225	)		24.80
Forfeited		(694	)		33.48
Unvested as of December 31, 2021		5,597		$	51.54

At December 31, 2021, the Company had unrecognized stock-based compensation relating to restricted stock of approximately $265.4 million, which is expected to be recognized over a weighted-average period of 2.8 years.

In September 2016, the Company established an ESPP with 8.0 million shares of Class A common stock available for issuance. As of December 31, 2021, 7.6 million shares remained available for grant under this plan. The number of shares authorized for grant is subject to increase each year on January 1, equal to the lesser of (a) 8.0 million shares, (b) 1% of the Class A common stock outstanding (on an as-converted basis) on the final day of the immediately preceding calendar year, and (c) such smaller number of

shares as determined by the Company’s board of directors. On January 1, 2022, the number of shares available for issuance under the Company’s ESPP increased by 4.4 million shares in accordance with plan provisions.

Under the ESPP, all eligible employees are permitted to authorize payroll deductions of up to 100% of their compensation to purchase shares of Class A common stock, subject to applicable ESPP and statutory limits. The ESPP provides for offering periods generally up to two years, with purchases occurring and new offering periods commencing generally every six months. ESPP purchases generally occur on May 15th and November 15th each year. At each purchase date, employees are able to purchase shares at 85% of the lower of (1) the closing market price per share of Class A common stock on the employee’s enrollment into the applicable offering period and (2) the closing market price per share of Class A common stock on the purchase date. The ESPP has an automatic reset feature, whereby the offering period resets if the fair value of the Company’s common stock on a purchase date is less than that on the original offering date.

The fair value of ESPP shares was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year ended December 31,
	2021			2020			2019
Expected term (years)		0.6			0.6			0.7
Expected volatility		62.3	%		61.9	%		53.2	%
Risk-free interest rate		0.09	%		0.40	%		2.08	%
Estimated dividend yield		—	%		—	%		—	%

The ESPP has a six-month holding period with respect to common stock purchases. Due to the holding period, the Company applies a discount to reflect the non-transferability of the shares. Stock-based compensation expense related to ESPP was $62.2 million, $33.0 million and $25.7 million for the years ended December 31, 2021, 2020 and 2019, respectively. At December 31, 2021, the Company had unrecognized stock-based compensation relating to ESPP awards of approximately $41.4 million, which is expected to be recognized over a weighted-average period of 0.5 years.