Our 2002 Stock Plan (the "2002 Plan") was approved in April 2002 and amended in June 2011. In August 2012 and in connection with the adoption of the 2012 Plan, shares authorized for issuance under the 2002 Plan were cancelled, except for those shares reserved for issuance upon exercise of outstanding stock options. Any outstanding stock options granted under the 2002 Plan remain outstanding, subject to the terms of the 2002 Plan, until such shares are issued under those awards (by exercise of stock options) or until the awards terminate or expire by terms.

Grants under the 2002 Plan generally vest ratably over a four years period from the vesting commencement date and expire ten years from grant date. Original grants under the 2002 Plan were for "common stock". Pursuant to the Twelfth Amended and Restated Articles of Incorporation authorized in July 2018, all such shares automatically converted to Class B shares of common stock. As of December 31, 2021, options to purchase 48,777 shares of Class B common stock were outstanding with a weighted average exercise price of $30.29 per share. The 2002 Stock Plan has been canceled but continues to govern outstanding option grants under the 2002 Plan.

Our 2012 Equity Incentive Plan (the "2012 Plan") was approved in August 2012. The 2012 Plan provided for the grant of incentive stock options, non-statutory stock options, stock appreciation rights and RSUs, all of which may be granted to employees, including officers, and to non-employee directors and consultants except we may grant incentive stock options only to employees.

Grants under the 2012 Plan generally vest ratably over a four years period from the vesting commencement date and expire ten years from grant date. Original grants under the 2012 Plan were for "common stock". Pursuant to the Twelfth Amended and Restated Articles of Incorporation authorized in July 2018, all such shares automatically converted to Class B shares of common stock. As of December 31, 2021, stock options to purchase 6,891,128 shares of Class B common stock were outstanding with a weighted average exercise price of $27.52 per share and no shares were available for future grant. The 2012 Equity Incentive Plan has been canceled but continues to govern outstanding option grants under the 2012 Plan.

The 2018 Equity Incentive Plan (the "2018 Plan") was approved in April 2018. The 2018 Plan became effective upon the IPO and serves as the successor to the 2012 Plan. The 2018 Plan authorizes the award of stock options, restricted stock awards, stock appreciation rights, RSUs, PSUs and stock bonuses. The 2018 Plan provides for the grant of awards to employees, directors, consultants, independent contractors and advisors provided the consultants, independent contractors, directors and advisors render services not in connection with the offer and sale of securities in a capital-raising transaction. The exercise price of stock options is at least equal to the fair market value of Class A common stock on the date of grant. Grants under the 2018 Plan generally vest ratably over a three or four years from the vesting commencement date and expire ten years from grant date.

The 2018 Plan allows for an annual increase on January 1, of each of 2019 through 2028, by the lesser of (a) four percent (4%) of the number of Class A common stock, Class B common stock, and common stock equivalents (including options, RSUs, warrants and preferred stock on an as-converted basis) issued and outstanding on each December 31 immediately prior to the date of increase, and (b) such number of shares determined by the Board of Directors.

As of December 31, 2021, stock options to purchase 3,797,391 shares of Class A common stock were outstanding with a weighted average exercise price of $9.70 per share and 8,367,663 shares of outstanding RSUs that may be settled for Class A common stock which were granted pursuant to the 2018 Plan. As of December 31, 2021, we had 23,999,768 shares reserved for issuance under the 2018 Plan.

We used the following weighted-average assumptions in applying the Black-Scholes valuation model for determination of option valuation:


	Years Ended December 31,
		2021	2020	2019

Risk-free interest rate		—	0.6%	1.7% - 2.6%
Expected term (years)		—	6.6	6.4 - 6.7
Expected dividend yield		—	—	—
Expected volatility		—	71.0%	45.7% - 50.2%


	Years Ended December 31,
		2021		2020		2019

Cost of revenue		$	13,811	$	17,475	$	45,429
Research and development		20,274		19,037		40,949
Sales and marketing		17,085		10,997		32,478
General and administrative		24,962		26,384		77,435
		$	76,132	$	73,893	$	196,291


	Outstanding Options
	Number of Shares	Weighted Average Exercise Price		Remaining Contractual Life (Years)	Aggregate Intrinsic Value

					(in thousands)




Balances at December 31, 2019	17,837,316	$	20.76	6.9	$	14,964
Granted	200,000	7.30
Exercised	(1,341,324)	11.18
Cancelled	(1,341,721)	22.49
Balances at December 31, 2020	15,354,271	21.27		6.0	129,855

Exercised	(3,460,364)	23.05
Cancelled	(1,156,612)	16.33
Balances at December 31, 2021	10,737,295	21.23		5.2	60,304
Vested and expected to vest at December 31, 2021	10,620,061	21.36		5.2	58,772
Exercisable at December 31, 2021	8,858,957	23.67		4.8	36,441

We did not grant options in the year ended December 31, 2021 and we granted 200,000 options of Class A common stock during the year ended December 31, 2020, and the weighted average grant-date fair value of those granted awards was $7.30 per share.

As of December 31, 2021 and 2020, we had unrecognized compensation costs related to unvested stock options of $6.2 million and $20.7 million, respectively. This cost is expected to be recognized over the remaining weighted-average period of 0.9 years and 1.8 years, respectively. Cash received from stock options exercised totaled $79.7 million and $15.0 million for the years ended December 31, 2021 and 2020, respectively.


	Number of Awards Outstanding	Weighted Average Grant Date Fair Value





Unvested Balance at December 31, 2019	10,112,266	$	17.29
Granted	4,744,467	12.43
Vested	(7,806,038)	17.48
Forfeited	(631,907)	14.93
Unvested Balance at December 31, 2020	6,418,788	$	13.71
Granted	6,475,536	25.82
Vested	(2,904,996)	17.04
Forfeited	(1,621,664)	20.97
Unvested Balance at December 31, 2021	8,367,664	20.52

Stock Awards - The estimated fair value of RSUs and PSUs is based on the fair value of our Class A common stock on the date of grant. For the years ended December 31, 2021 and 2020, we recognized $50.1 million and $44.1 million of stock-based compensation costs for stock awards, respectively.

As of December 31, 2021 and 2020, we had $114.9 million and $59.8 million of unrecognized stock-based compensation cost related to unvested stock awards, expected to be recognized over a weighted average period of 2.3 years and 2.2 years, respectively.

In November 2019, the Board approved stock options ("2019 Executive Awards") to certain executive staff. The 2019 Executive Awards were granted pursuant to the 2018 Plan and consist of three vesting tranches with a vesting schedule based on the attainment of market conditions and assuming continued employment and service through each vesting date. Stock-based compensation costs associated with the 2019 Executive Awards are recognized over the service period, even though no tranches of the 2019 Performance Awards vest unless a market condition is achieved. The grant date fair value of the options is determined using a Monte Carlo simulation.

In June 2020, the Board approved stock awards ("2020 Executive Awards") to certain executive staff. The 2020 Executive Awards were PSUs granted pursuant to the 2018 Plan and consist of three vesting tranches with an annual vesting schedule based on the attainment of performance conditions and assuming continued employment and service through each vesting date. Stock-based compensation costs associated with the 2020 Executive Awards is recognized over the service period as we evaluate the probability of the achievement of the performance conditions.

In June 2021, the Board approved stock awards ("2021 Executive Awards") to certain executive staff. The 2021 Executive Awards were PSUs granted pursuant to the 2018 Plan and consist of three vesting tranches with an annual vesting schedule based on the attainment of performance conditions and assuming continued employment and service through each vesting date. Stock-based compensation costs associated with the 2021 Executive Awards is recognized over the service period as we evaluate the probability of the achievement of the performance conditions.

In May 2021, we issued RSUs and PSUs to our Chief Executive Officer. The RSUs will vest in equal annual installments over five years from the grant date. A portion of the PSUs can be earned based on achieving certain financial performance goals and another portion can be earned based upon achieving certain progressive stock price hurdles. Any shares issued under the PSU awards will be subject to a two-year post-vest holding period in which the award holder will be restricted from selling any shares (net of shares settled for taxes). As of December 31, 2021, the unamortized compensation expense for the RSUs and PSUs was $24.0 million. Actual compensation expense is dependent on the performance of the PSUs that vest based upon a performance condition. We estimated the fair value of the PSUs that vest based on a market condition on the date of grant using a Monte Carlo simulation with the following assumptions: (i) expected volatility of 71.2%, (ii) risk-free interest rate of 1.6%, and (iii) no expected dividend yield.

In April 2018, we adopted the 2018 ESPP. The 2018 ESPP became effective upon our initial public offering ("IPO") in July 2018. The 2018 ESPP is intended to qualify under Section 423 of the Internal Revenue Code. The aggregate number of our shares that may be issued over the term of our ESPP is 33,333,333 Class A common stock. A total of 3,333,333 shares of our Class A common stock were initially reserved for issuance under the plan. The number of shares reserved for issuance under the 2018 ESPP will increase automatically on the 1st day of January of each of the first nine years following the first offering date by the number of shares equal to one percent (1%) of the total number of Class A common stock, Class B common stock and common stock equivalents (including options, RSUs, warrants and preferred stock on an as converted basis) issued and outstanding on the immediately preceding December 31 (rounded down to the nearest whole share); provided, that the Board of Directors or the Compensation Committee may in its sole discretion reduce the amount of the increase in any particular year.

The 2018 ESPP allows eligible employees to purchase shares, subject to purchase limits of 2,500 shares during each six month period or $25,000 worth of stock for each calendar year, of our Class A common stock through payroll deductions at a price per share equal to 85% of the lesser of the fair market value of our Class A common stock (i) on the first trading day of the applicable offering date and (ii) the last trading day of each purchase date.

During the years ended December 31, 2021 and 2020, we recognized $7.7 million and $5.7 million of stock-based compensation costs for the 2018 ESPP, respectively. We issued 1,945,305 shares in the year ended December 31, 2021. During the year ended December 31, 2021, we added an additional 1,902,572 shares and there were 2,544,668 shares available for issuance as of December 31, 2021.