The 2021 Equity Incentive Plan (“2021 Plan”) provides for the issuance of incentive and nonqualified stock options, stock appreciation rights, restricted stock, restricted stock units (“RSUs”), performance-based restricted stock units (“PSUs”), and other awards, to employees, directors, consultants, and advisors. Pursuant to the evergreen provisions of the 2021 Plan, the Board of Directors approved an automatic increase of 8,168,075 additional shares of Class A common stock reserved and available for issuance under the 2021 Plan effective as of January 1, 2024.

As of June 30, 2024 and December 31, 2023 the maximum number of shares authorized for issuance to participants under the 2021 Plan was 49,148,955 and 40,556,635, respectively. As of June 30, 2024 and December 31, 2023, the number of shares available for issuance to participants under the 2021 Plan was 31,286,770 and 25,029,007, respectively.

The total fair value of RSUs vested during the six months ended June 30, 2024 was $8.1 million. Future stock-based compensation expense for unvested RSUs awarded as of June 30, 2024 was approximately $62.3 million and is expected to be recognized over a weighted-average period of 2.65 years.

In February 2023, we made grants to executives in the form of PSUs (“2023 PSUs”) that will vest over three years based on the achievement of specified financial targets at the end of a one-year performance period, subject to the executive’s continuous service. The target number of shares underlying the 2023 PSUs was determined based on the higher of (a) the 30-trading day average price preceding the grant date or (b) the floor price as determined by the Compensation Committee of the Board of Directors for the calendar year. Based on the actual financial metrics achieved relative to the target financial metrics for the year ended December 31, 2023, the number of PSUs issued were 103.86% of the target PSUs. Accordingly, 150,036 shares vested for the six months ended June 30, 2024 upon meeting the time-based vesting requirement. The remaining eligible shares will vest according to the time-based service requirements, subject to the applicable executive’s continued service as of each vesting date. The fair value of the 2023 PSUs is calculated based on the stock price on the date of grant.

In March 2024, we made additional PSU grants to executives (“2024 PSUs”) that will vest over approximately three years based upon achievement of either (a) certain stock price targets or (b) our target total shareholder return (“TSR”), relative to the TSR of companies in the Russell 2000 Index over the specified performance period, in each case, subject to the executive’s continuous service through the last day of the applicable performance period. Depending on achievement of the market-based metrics, the number of PSUs issued could range from 0% to 200% of the target PSUs. The fair value of the 2024 PSUs is determined using a Monte Carlo simulation model on the date of the grant.

Stock-based compensation expense is recognized over the requisite service period using either the straight-line method or the accelerated attribution method (depending on the award), and is adjusted based on actual forfeitures as necessary.

The total fair value of PSUs vested during the six months ended June 30, 2024 was $0.8 million. Future stock-based compensation expense for unvested PSUs as of June 30, 2024 was approximately $13.3 million and is expected to be recognized over a weighted-average period of 2.50 years.

The employee stock purchase plan (“ESPP”) current offering period began in June 2024 and ends in December 2024. Pursuant to the evergreen provisions of the ESPP, the Board of Directors approved an automatic increase of 1,084,696 additional shares of Class A common stock reserved and available for issuance under the ESPP effective as of January 1, 2024. As of June 30, 2024, a total of 6,402,450 shares are available for issuance to employees under the ESPP. For the six months ended June 30, 2024 and 2023, we recorded approximately $0.4 million and $0.7 million of compensation expense associated with our ESPP, respectively.

The classification of stock-based compensation expense, which includes expense for stock options, RSUs, PSUs, and ESPP charges, by line item within the condensed consolidated statements of operations was as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Cost of revenue - platform	$	1,302	$	1,673	$	2,813	$	3,498
Cost of revenue - professional services and other	49		172		174		363
Research and development	2,658		3,555		5,679		8,102
General and administrative	4,885		5,600		9,565		10,587
Sales and marketing	1,522		2,056		3,025		4,550
Restructuring charges	—		1,728		—		1,728
Total stock-based compensation expense	$	10,416	$	14,784	$	21,256	$	28,828