The 2013 Equity Plan authorizes the issuance of various types of share-based awards to the Company’s employees, officers, directors, and other eligible participants. In the second quarter of 2021, the Board of Directors authorized and the stockholders approved an amendment to the 2013 Equity Plan to increase the total number of shares of the Company’s class A common stock authorized for issuance under the 2013 Equity Plan from 2,300,000 shares to 2,750,000 shares. As of December 31, 2021, there were 549,269 shares of class A common stock reserved and available for future issuance under the 2013 Equity Plan.

Under the 2013 Equity Plan, the Company has issued stock option awards, share-settled restricted stock units, other stock-based awards, and cash-settled restricted stock units. Regardless of the type of award issued, any shares issued under the 2013 Equity Plan may consist in whole or in part of authorized but unissued shares or treasury shares. No awards may be issued more than 10 years after the 2013 Equity Plan’s effective date. In determining related share-based compensation expense for any award under the 2013 Equity Plan, the

Company has made an accounting policy election to account for forfeitures of awards as they occur and therefore share-based compensation expense presented below has not been adjusted for any estimated forfeitures.

Stock options that are granted under the 2013 Equity Plan must have an exercise price equal to at least the fair market value of the Company’s class A common stock on the date of grant, become exercisable as established by the Board of Directors or the Compensation Committee, and expire no later than 10 years following the date of grant. The Company recognizes share-based compensation expense associated with such stock option awards on a straight-line basis over the award’s requisite service period (generally, the vesting period). The stock option awards granted to date vest in equal annual installments over an approximately four-year vesting period (unless accelerated in connection with a change in control event under specified conditions as set forth in the applicable option agreement or otherwise in accordance with provisions of the 2013 Equity Plan or applicable option agreement).

Share-based compensation expense related to stock option awards is based on the fair value of the stock option awards on the date of grant, as estimated using the Black-Scholes valuation model. The Black-Scholes valuation model requires the input of certain management assumptions, including the expected term, expected stock price volatility, risk-free interest rate, and expected dividend yield. The Company estimates the term over which option holders are expected to hold their stock options by using the simplified method for “plain-vanilla” stock option awards because the Company’s stock option exercise history does not provide a reasonable basis to compute the expected term for stock options granted under the 2013 Equity Plan. Beginning in 2021, as a result of the significant increase in the Company’s stock price volatility, the Company established estimates for the expected stock price volatility by calculating a blended rate from the historical stock price volatility of its class A common stock and the implied volatility of the Company’s traded financial instruments with similar terms to the respective award. For stock options granted prior to 2021, the Company relied exclusively on its historical stock price volatility using a simple average calculation method to estimate the expected stock price volatility over the expected term because the Company believed at the date of grant that future volatility was unlikely to differ from the past. The risk-free interest rate is based on U.S. Treasury securities with terms that approximate the expected term of the stock options. The expected dividend yield is zero, as the Company has not previously declared cash dividends and does not currently intend to declare cash dividends in the foreseeable future. These assumptions are based on management’s best judgment, and changes to these assumptions could materially affect the fair value estimates and amount of share-based compensation expense recognized.

As of December 31, 2021, there were options to purchase 1,166,754 shares of class A common stock outstanding under the 2013 Equity Plan. The following table summarizes the Company’s stock option activity (in thousands, except per share data and years) for the periods indicated:

	Stock Options Outstanding
				Weighted Average		Aggregate		Weighted Average
				Exercise Price		Intrinsic		Remaining Contractual
	Shares			Per Share		Value		Term (Years)
Balance as of January 1, 2019		1,480		$	137.16
Granted		470			150.88
Exercised		(51	)		128.17	$	799
Forfeited/Expired		(265	)		135.88
Balance as of December 31, 2019		1,634			141.60
Granted		118			146.76
Exercised		(348	)		146.80	$	29,994
Forfeited/Expired		(247	)		146.63
Balance as of December 31, 2020		1,157			139.48
Granted		305			676.10
Exercised		(269	)		151.19	$	163,427
Forfeited/Expired		(26	)		499.11
Balance as of December 31, 2021		1,167		$	268.74
Exercisable as of December 31, 2021		576		$	131.39	$	237,948	3.5
Expected to vest as of December 31, 2021		591		$	402.66		122,964	8.4
Total		1,167		$	268.74	$	360,912	6.0

Stock options outstanding as of December 31, 2021 are comprised of the following range of exercise prices per share (in thousands, except per share data and years):

	Stock Options Outstanding at December 31, 2021
			Weighted Average		Weighted Average
			Exercise Price		Remaining Contractual
Range of Exercise Prices per Share	Shares		Per Share		Term (Years)
$121.43 - $200.00		880	$	135.94		4.9
$400.01 - $500.00		20	$	470.00		9.4
$600.01 - $691.23		267	$	691.23		9.1
Total		1,167	$	268.74		6.0

An aggregate of 200,625, 200,000, and 216,250 stock options with an aggregate grant date fair value of $11.0 million, $11.2 million, and $12.6 million vested during the years ended December 31, 2021, 2020, and 2019, respectively.

The weighted average grant date fair value of stock option awards using the Black-Scholes valuation model was $372.05, $49.68, and $54.36 for each share subject to a stock option granted during the years ended December 31, 2021, 2020, and 2019, respectively, based on the following assumptions:

The Company recognized approximately $32.0 million, $10.1 million, and $10.1 million in share-based compensation expense for the years ended December 31, 2021, 2020, and 2019, respectively, from stock options granted under the 2013 Equity Plan. As of December 31, 2021, there was approximately $96.1 million of total unrecognized share-based compensation expense related to unvested stock options. As of December 31, 2021, the Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 3.0 years.

During the fourth quarter of 2020, the Company began granting share-settled restricted stock units under the 2013 Equity Plan. The share-settled restricted stock units entitle recipients to receive a number of shares of the Company’s class A common stock over a vesting period, as specified in the applicable restricted stock unit agreement. Although the Company may in its sole discretion elect to pay fully or partially in cash in lieu of settling solely in shares, it does not currently intend to do so.

Share-based compensation expense related to share-settled restricted stock units is based on the fair value of the Company’s class A common stock on the date of grant. The Company recognizes share-based compensation expense associated with such share-settled restricted stock unit awards on a straight-line basis over the award’s requisite service period (generally, the vesting period). The share-settled restricted stock unit awards granted to date vest in equal annual installments over a four-year period (unless accelerated in connection with a change in control event under specified conditions as set forth in the applicable restricted stock unit agreement or otherwise in accordance with provisions of the 2013 Equity Plan or applicable restricted stock unit agreement). Upon vesting of the share-settled restricted stock units, the Company covers the minimum tax withholding obligation by withholding shares with equivalent

value based on the closing stock price on the vesting date. The Company then pays the withholding tax obligation to the appropriate taxing authorities which is reflected as a financing activity on the Consolidated Statements of Cash Flows.

As of December 31, 2021, there were 105,115 share-settled restricted stock units outstanding under the 2013 Equity Plan. The following table summarizes the Company’s share-settled restricted stock unit activity (in thousands) for the periods indicated:

	Share-Settled Restricted Stock Units Outstanding
				Aggregate
				Intrinsic
	Units			Value
Balance as of January 1, 2020		0
Granted		76
Vested		0		$	0
Forfeited		(2	)
Balance as of December 31, 2020		74
Granted		58
Vested		(17	)	$	13,803
Forfeited		(10	)
Balance as of December 31, 2021		105
Expected to vest as of December 31, 2021		105		$	57,234

During the year ended December 31, 2021, 17,004 share-settled restricted stock units having an aggregate grant date fair value of $3.3 million vested, 5,857 shares were withheld to satisfy tax obligations, resulting in 11,147 issued shares. No share-settled restricted stock units vested during the year ended December 31, 2020. The weighted average grant date fair value of share-settled restricted stock units granted during the years ended December 31, 2021 and 2020 was $736.46 and $192.43, respectively, based on the fair value of the Company’s class A common stock. The Company recognized approximately $8.0 million and $0.5 million in share-based compensation expense for the years ended December 31, 2021 and 2020, respectively, from share-settled restricted stock units granted under the 2013 Equity Plan. No share-settled restricted stock units were granted under the 2013 Equity Plan prior to the fourth quarter of 2020. As of December 31, 2021, there was approximately $44.6 million of total unrecognized share-based compensation expense related to unvested share-settled restricted stock units. As of December 31, 2021, the Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 3.4 years.

During 2021, the Company granted 9,000 “other stock-based awards” under the 2013 Equity Plan. Other stock-based awards were not granted in 2020 or 2019. As of December 31, 2021, there were a total of 10,250 other stock-based awards outstanding under the 2013 Equity Plan. These other stock-based awards are similar to stock options, except these awards are settled in cash only and not in shares of the Company’s class A common stock.

During 2021, the Company granted 900 cash-settled restricted stock units under the 2013 Equity Plan. Cash-settled restricted stock units were not granted prior to 2021. As of December 31, 2021, there were a total of 900 cash-settled restricted stock units outstanding under the 2013 Equity Plan. These cash-settled restricted stock units are similar to the Company’s share-settled restricted stock units, except they are settled in cash only and not in shares of the Company’s class A common stock.

Both the other stock-based awards and the cash-settled restricted stock units are classified as liabilities in the Company’s Consolidated Balance Sheets due to the required cash settlement feature and the fair value of the awards is remeasured each quarterly reporting period. The Company recognized approximately $1.4 million in share-based compensation expense from other stock-based awards and cash-settled restricted stock units for the year ended December 31, 2021. The Company recognized approximately $0.6 million in share-based compensation expense from other stock-based awards for the year ended December 31, 2020. For the year ended December 31, 2019 share-based compensation expense from other stock-based awards was not material. As of December 31, 2021, there was approximately $2.5 million of total unrecognized share-based compensation expense related to other stock-based awards and cash-settled restricted stock units. The Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 2.9 years, subject to additional fair value adjustments through the earlier of settlement or expiration.

During the first quarter of 2021, the Company adopted the 2021 ESPP, and in the second quarter of 2021, the Company’s stockholders approved the 2021 ESPP. The purpose of the 2021 ESPP is to provide eligible employees of the Company and certain of its subsidiaries with opportunities to purchase shares of the Company’s class A common stock, commencing at such time and on such dates as the Board of Directors of the Company shall determine. An aggregate of 100,000 shares of the Company’s class A common stock has been authorized for issuance under the 2021 ESPP.

Unless otherwise determined by the Board of Directors, shares are purchased at a price equal to 85% of the lesser of the closing price of the Company’s class A common stock on the first or last business day of the offering period, respectively. Share-based compensation expense is based on the grant date fair value, which consists of the intrinsic value of the 15% discounted share purchase rights and the fair value of the look-back provision using the Black-Scholes valuation model, recognized on a straight-line basis over the offering period. The grant date is the offering period commencement date.

The first offering period under the 2021 ESPP commenced on February 16, 2021 and ended on August 15, 2021. A second offering period under the 2021 ESPP commenced on September 1, 2021 and will end on February 28, 2022. During the year ended December 31, 2021, the Company recognized approximately $2.6 million in share-based compensation expense related to the 2021 ESPP. As of December 31, 2021, there was approximately $0.5 million of total unrecognized share-based compensation expense related to the 2021 ESPP. The Company expects to recognize this remaining share-based compensation expense over a period of approximately 0.2 years. During the year ended December 31, 2021, 4,612 shares of class A common stock were issued in connection with the 2021 ESPP. As of December 31, 2021, 95,388 shares of the Company’s class A common stock remained available for issuance under the 2021 ESPP.

During the year ended December 31, 2021, the Company recognized tax benefits on exercises of stock options and vesting of share-settled restricted stock units of approximately $37.7 million and tax benefits on share-based compensation expense of approximately $8.2 million, for a total tax benefit of $45.9 million related to the Company’s equity plans. During the year ended December 31, 2020, the Company recognized tax benefits on exercises of stock options of approximately $3.2 million and tax benefits on share-based compensation expense of approximately $2.0 million, for a total tax benefit of $5.2 million related to the Company’s equity plans. The tax benefits related to the Company’s equity plans were not material for the year ended December 31, 2019.