The Company has two classes of common stock, Class A and Class B. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to ten votes per share. Shares of Class B common stock may be converted into Class A common stock at any time at the option of the stockholder, and are automatically converted upon the sale or transfer to Class A common stock, subject to certain limited exceptions.

During the three months ended March 31, 2020, 87,517,942 shares of Class B common stock were converted into Class A common stock.

As of March 31, 2020, the Company had authorized 2,000,000,000 shares of Class A common stock and 310,000,000 shares of Class B common stock, each at a par value per share of $0.00001, of which 153,495,803 shares of Class A common stock and 145,238,917 shares of Class B common stock were issued and outstanding.

The Company has two equity incentive plans, the 2012 equity incentive plan (the “2012 Plan”) and the 2019 equity incentive plan (the “2019 Plan”). In connection with the IPO, the Company ceased granting awards under the 2012 Plan, and all shares that remained available for issuance under the 2012 Plan at that time were transferred to the 2019 Plan. Under the 2019 Plan, the Board and any other committee or subcommittee of the Board may grant stock options, stock appreciation rights (“SARs”), restricted stock awards (“RSAs”), restricted stock units (“RSUs”), and performance-based and other awards, each valued or based on the Company’s Class A common stock, to employees, consultants, and advisors of the Company. As of March 31, 2020, there were 46,421,549 shares available for grant under the 2019 Plan.

	Number Of Options Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in Years)
Balance—December 31, 2019		36,384,767		$	2.96		7.6
Options granted		14,600		$	41.19
Options exercised		(2,347,770	)	$	1.20
Options forfeited		(180,499	)	$	4.58
Balance—March 31, 2020		33,871,098		$	3.09		7.4
Exercisable—March 31, 2020		21,804,073		$	2.30		6.9

As of March 31, 2020, there were 35,300 shares of Class A common stock and 33,835,798 shares of Class B common stock issuable upon the exercise of options outstanding. As of December 31, 2019, there were 20,700 shares of Class A common stock and 36,364,067 shares of Class B common stock issuable upon the exercise of options outstanding.

Total compensation cost related to unvested options not yet recognized was approximately $83.1 million and $90.5 million as of March 31, 2020 and December 31, 2019, respectively. The weighted average period over which this compensation cost related to unvested employee options will be recognized is 2.5 years and 2.7 years as of March 31, 2020 and December 31, 2019, respectively.

The weighted average grant-date fair value of options granted during the three months ended March 31, 2020 and March 31, 2019, was $16.55 and $3.34, respectively. The Company received approximately $2.8 million and $1.8 million in cash proceeds from options exercised during the three months ended March 31, 2020 and March 31, 2019, respectively. The intrinsic value of options exercised during the three months ended March 31, 2020 and March 31, 2019 was approximately $86.5 million and $16.8 million, respectively. The aggregate fair value of options vested during the three months ended March 31, 2020 and 2019 was $3.8 million and $1.8 million, respectively.

Common stock purchased pursuant to an early exercise of stock options is not deemed to be outstanding for accounting purposes until those shares vest. The consideration received for an exercise of an option is considered to be a deposit of the exercise price and the related dollar amount is recorded as a liability. The shares issued upon the early exercise of these unvested stock option awards, which are reflected as exercises in the table above, are considered to be legally issued and outstanding on the date of exercise. Upon termination of service, the Company may repurchase unvested shares acquired through early exercise of stock options at a price equal to the price per share paid upon the exercise of such options. The Company has recorded liabilities related to early exercises of 1,039,500 shares of common stock and 1,239,750 shares of common stock as of March 31, 2020 and December 31, 2019, respectively.

Restricted Stock Units

The following table summarizes the activity for the Company's unvested RSUs:

	Shares			Weighted-Average Fair Value
Balance—December 31, 2019		647,094		$	36.08
Granted		696,740		$	43.12
Vested		—		$	—
Forfeited/canceled		(27,610	)	$	38.32
Balance—March 31, 2020		1,316,224		$	39.76

In November 2019, the Company granted 244,445 restricted shares of Class A common stock, which are subject to service-based vesting conditions over approximately four years. Total compensation cost related to unvested RSUs and restricted shares of common stock not yet recognized was approximately $56.4 million and $30.4 million as of March 31, 2020 and December 31, 2019, respectively. The weighted average period over which this compensation cost related to unvested RSUs and restricted shares will be recognized is 3.8 years and 3.9 years as of March 31, 2020 and December 31, 2019, respectively.

Employee Stock Purchase Plan

In September 2019, the Board adopted and approved the 2019 Employee Stock Purchase Plan (the “ESPP”), which became effective on the date of the final prospectus for the Company’s IPO (the “Final Prospectus”). The ESPP initially reserved and authorized the issuance of up to a total of 6,725,000 shares of Class A common stock to participating employees, subject to periodic automatic increases in the amount of shares reserved under the ESPP. As of March 31, 2020, 9,688,869 shares of Class A common stock remain available for grant under the ESPP. The initial offering period began on the date of the Final Prospectus and will end on May 15, 2020. On each purchase date, eligible employees will purchase the shares at a price per share equal to 85% of the lesser of (1) the $27.00 initial public offering price of the Company’s Class A common stock or (2) the fair market value of the Company’s Class A common stock on the purchase date, as defined in the ESPP.

The Company recognized $1.0 million of stock-based compensation expense related to the ESPP during the three months ended March 31, 2020, beginning upon the IPO in September 2019. As of March 31, 2020, $6.4 million has been withheld on behalf of employees for a future purchase under the ESPP due to the timing of payroll deductions. There were no purchases for the three months ended March 31, 2020 related to the ESPP.

Stock-Based Compensation

The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock options on the date of grant. The Company recognizes and measures compensation expense for all stock-based payment awards granted to employees, directors, and nonemployees based on the fair value of the awards on the date of grant. The determination of the grant date fair value using an option-pricing model is affected by the estimated fair value of the Company’s common stock as well as assumptions regarding a number of other complex and subjective variables. These variables include expected stock price volatility over the expected term of the award, actual and projected employee stock option exercise behaviors, the risk-free interest rate for the expected term of the award and expected dividends. The fair value of RSUs is determined by the closing price on the date of grant of the Company’s Class A common stock, as reported on The Nasdaq Global Select Market. The Company estimates the fair value of the rights to acquire stock under the ESPP using the Black-Scholes option pricing model. Stock-based compensation is recognized on a straight-line basis over the requisite service period and account for forfeitures as they occur.

Stock-based compensation expense was included in the condensed consolidated statement of operations as follows (in thousands):

	Three Months Ended March 31,
	2020		2019
Cost of revenue	$	231	$	99
Research and development		5,847		786
Sales and marketing		3,074		729
General and administrative		2,908		831
Stock-based compensation, net of amounts capitalized		12,060		2,445
Capitalized stock-based compensation expense		103		52
Total stock-based compensation expense	$	12,163	$	2,497