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-year 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, 2020, options to purchase 1,265,656 shares of Class B common stock were

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 restricted stock awards ("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-year 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, 2020, stock options to purchase 8,877,792 shares of Class B common stock were outstanding with a weighted average exercise price of $27.43 per share and no shares were available for future grant. As of December 31, 2020, we had outstanding RSUs that may be settled for 504,034 shares of Class B common stock under the plan. The 2012 Equity Incentive Plan has been canceled; however, it continues to govern outstanding grants under the 2012 Equity Incentive Plan.

The 2018 Equity Incentive Plan (the "2018 Plan") was approved in April 2018. The 2018 Plan became effective upon the IPO and will serve 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 four-year period 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, 2020, stock options to purchase 5,210,823 shares of Class A common stock were outstanding with a weighted average exercise price of $9.48 per share and 5,914,754 shares of outstanding RSUs that may be settled for Class A common stock which were granted pursuant to the 2018 Plan.


	Years Ended December 31,
		2020	2019	2018

Risk-free interest rate		0.6%	1.7% - 2.6%	2.5% - 3.1%
Expected term (years)		6.6	6.4 - 6.7	6.2 - 6.7
Expected dividend yield		—	—	—
Expected volatility		71.0%	45.7% - 50.2%	52.4% - 56.1%


	Years Ended December 31,
		2020		2019		2018

Cost of revenue		$	17,475	$	45,429	$	29,680
Research and development		19,037		40,949		39,029
Sales and marketing		10,997		32,478		32,284
General and administrative		26,384		77,435		67,489
		$	73,893	$	196,291	$	168,482


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

					(in thousands)
Balances at December 31, 2018	14,558,420	$	25.93	6.8	$	3,084
Granted	4,956,064	5.60
Exercised	(358,564)	4.26
Cancelled	(1,318,604)	25.33
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
Vested and expected to vest at December 31, 2020	14,976,706	21.55		5.9	122,813
Exercisable at December 31, 2020	10,311,316	26.37		4.9	39,569

We granted 200,000 and 4,956,064 options of Class A common stock during the years ended December 31, 2020 and 2019, and the weighted average grant-date fair value of the awards was $7.30 per share and $5.60 per share, respectively.

As of December 31, 2020 and 2019, we had unrecognized compensation costs related to unvested stock options of $20.7 million and $41.9 million, respectively. This cost is expected to be recognized over the remaining weighted-average period of 1.8 years and 2.8 years, respectively. Cash received from stock options exercised totaled $15.0 million and $1.5 million for the years ended December 31, 2020 and 2019, respectively.


	Number of Awards Outstanding	Weighted Average Grant Date Fair Value

Unvested Balance at December 31, 2018	16,784,800	$	18.74
Granted	3,219,959	11.81
Vested	(8,921,807)	18.03
Forfeited	(970,686)	17.34
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

Restricted Stock Units - The estimated fair value of RSU awards is based on the fair value of our Class A common stock on the date of grant. For the years ended December 31, 2020, 2019 and 2018, we recognized $44.1 million, $141.3 million and $142.4 million of stock-based compensation costs for RSUs, respectively.

As of December 31, 2020, we had $59.8 million of unrecognized stock-based compensation cost related to unvested RSUs. This cost is expected to be recognized over a weighted average period of 2.2 years. As of December 31, 2019, we had $52.0 million of unrecognized stock-based compensation cost related to unvested RSUs, which was expected to be recognized over a weighted average period of 1.1 years.

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 EIP 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 EIP 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.


						Plan Shares Available for Grant


Balances at December 31, 2018						17,457,847
Added to plan						7,585,422
Granted						(8,176,023)
Cancelled						2,289,290
Expired						(1,923,392)
Balances at December 31, 2019						17,233,144
Added to plan						7,179,751
Granted						(4,944,467)

Cancelled						1,965,801
Expired						(1,200,475)
Balances at December 31, 2020						20,233,754

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, 2020 and 2019, we recognized $5.7 million and $10.3 million of stock-based compensation costs for the 2018 ESPP, respectively. We issued 1,937,825 shares in the year ended December 31, 2020. During the year ended December 31, 2020, we added an additional 1,494,819 shares and there were 2,587,401 shares available for issuance as of December 31, 2020.