Amended and Restated 2004 Equity Incentive Plan—We granted stock options under our 2004 Equity Incentive Plan, as amended ("2004 Plan"), until July 26, 2017, when we terminated it in connection with our IPO. Accordingly, no shares are available for future issuance under our 2004 Plan. Our 2004 Plan continues to govern outstanding equity awards granted thereunder, all of which are fully vested. The term of each stock option under the plan is no more than 10 years, and each stock option generally vests over a four-year period.

2017 Equity Incentive Plan—Our 2017 Equity Incentive Plan ("2017 EIP") became effective on July 26, 2017 and provides for issuance of incentive and nonqualified common stock options and restricted stock units to employees, directors, officers, and consultants. The number of shares of common stock initially reserved for issuance under our 2017 EIP was 7,898,159. The number of shares reserved for issuance under our 2017 EIP will increase automatically on January 1 of each calendar year beginning on January 1, 2018, and continuing through January 1, 2028, by the number of shares equal to the lesser of 5% of the total outstanding shares of our common stock as of the immediately preceding December 31 or an amount determined by our board of directors. The term of each stock option and restricted stock unit under the plan will not exceed 10 years, and each award generally vests between two and four years.


	December 31,
	2023	2022
Stock options issued and outstanding	2,406,453	3,282,789
Restricted stock units outstanding	15,947,173	15,731,632
Shares available for future equity grants	7,991,532	7,951,616
Total shares reserved for future issuance	26,345,158	26,966,037

2017 Employee Stock Purchase Plan—Our 2017 Employee Stock Purchase Plan ("ESPP") was approved by the board of directors on July 27, 2017, and enables eligible employees to purchase shares of our common stock at a discount. Purchases will be accomplished through participation in discrete offering periods. We initially reserved 1,600,000 shares of common stock for issuance under our ESPP. The number of shares reserved for issuance under our ESPP will increase automatically on January 1 of each calendar year beginning after the first offering date and continuing through January 1, 2028, by the number of shares equal to the lesser of 1% of the total outstanding shares of our common stock as of the immediately preceding December 31 or an amount determined by our board of directors. On each purchase date, eligible employees will purchase our common stock at a price per share equal to 85% of the lesser of (i) the fair market value of our common stock on the first trading day of the offering period, and (ii) the fair market value of our common stock on the purchase date.


	December 31,
	2023	2022
Shares available for issuance at beginning of period	4,695,361	5,865,467
Shares issued during the period	(1,491,040)	(1,170,106)
Total shares available for issuance at end of period	3,204,321	4,695,361


	For the Offering Period beginning July 1, 2023	For the Offering Period beginning January 1, 2023
Expected life	0.5 years	0.5 years
Volatility	98.62%	98.94%
Risk-free interest rate	5.53%	4.77%
Dividend yield	—%	—%
Weighted-average grant date fair value	$5.22	$1.46


	Number Of Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (years)	Aggregate Intrinsic Value
Outstanding at January 1, 2023	3,282,789	$	9.10	2.90	$	1,145

Options exercised	(801,866)	2.99
Options expired	(74,470)	8.97
Outstanding at December 31, 2023	2,406,453	$	11.14	2.63	$	3,355
Options exercisable at December 31, 2023	2,406,453	$	11.14	2.63	$	3,355

The grant date fair value of our stock options was recorded as stock-based compensation over the stock options' vesting period. All outstanding options were fully vested as of December 31, 2023. We did not recognize any option-related expense during the year ended December 31, 2023.


	Restricted Stock Units	Weighted-Average Grant Date Fair Value
Outstanding at January 1, 2023	15,731,632	$	11.53
Granted	9,328,065	8.44
Vested	(6,955,493)	11.81
Forfeited or canceled	(2,157,031)	11.25
Outstanding or deferred at December 31, 2023(1)	15,947,173	$	9.64

(1) Starting with the restricted stock units granted to them in June 2019, our non-employee directors have the option to defer the issuance of common stock receivable upon vesting of such restricted stock units until 60 days following the day they are no longer providing services to us or, if earlier, upon a change in control transaction. The amount reported as vested excludes restricted stock units that have vested but whose settlement into shares have been deferred. The amount reported as outstanding or deferred as of December 31, 2023 includes these restricted stock units. As no further conditions exist to prevent the issuance of the shares of common stock underlying these restricted stock units, the shares are included in the basic and diluted weighted shares outstanding used to calculate net loss per share attributable to common stock. The amount of shares whose issuance have been deferred is not considered material and is not reported separately from stock-based compensation in our consolidated statements of changes in mezzanine equity and stockholders’ equity.

The grant date fair value of restricted stock units is recorded as stock-based compensation over the vesting period. As of December 31, 2023, there was $117,005 of total unrecognized stock-based compensation expense related to restricted stock units, which is expected to be recognized over a weighted-average period of 2.11 years.

As of December 31, 2023, there were 2,316,061 restricted stock units subject to performance and market conditions ("PSUs") outstanding at 100% of the target level. Depending on our achievement of the performance and market conditions, the actual number of shares of common stock issuable upon vesting of PSUs will range from 0% to 200% of the target amount. For each PSU recipient, the awards will vest only if the recipient is continuing to provide service to us upon our board of directors, or its compensation committee, certifying that we have achieved the PSUs' related performance or market conditions. Stock-based compensation expense for PSUs with performance conditions will be recognized when it is probable that the performance conditions will be achieved. For PSUs with market conditions, the market condition is reflected in the grant date fair value of the award and the expense is recognized over the life of the award. Stock-compensation expense associated with the PSUs is as follows:


	Year Ended December 31,
	2023		2022		2021
Expense associated with the current period	$	2,994	$	5,341	$	6,314
Expense due to reassessment of achievement related to prior periods	(553)		(267)		—
Total expense	$	2,441	$	5,074	$	6,314

Compensation Cost—The following table details, for each period indicated, (i) our stock-based compensation net of forfeitures, and the amount capitalized in internally developed software and (ii) includes changes to the probability of achieving outstanding performance-based equity awards, each as included in our consolidated statements of comprehensive loss:


	Year Ended December 31,
	2023		2022		2021
Cost of revenue	$	12,914	$	15,137	$	12,388
Technology and development(1)	33,111		26,365		21,172
Marketing	5,148		3,991		2,142
General and administrative	19,528		17,526		13,843
Stock-based compensation from continuing operations	70,701		63,019		49,545
Stock-based compensation from discontinued operations	234		5,238		5,177
Total stock-based compensation	$	70,935	$	68,257	$	54,722

(1) Net of $4,003, $3,660 and $4,059 of stock-based compensation expense capitalized for internally developed software for the years ended December 31, 2023, 2022 and 2021, respectively.