Equity incentive plans. The Company has outstanding equity grants from its three stock-based employee compensation plans: the 2014 Equity Incentive Plan (2014 Plan), the 2010 Equity Incentive Plan (2010 Plan) and the 2014 Employee Stock Purchase Plan (2014 ESPP). No new options or awards have been granted under the 2010 Plan since June 2014. Outstanding options and awards under the 2010 Plan continue to be subject to the terms and conditions of the 2010 Plan.

The 2014 Plan serves as a successor to the 2010 Plan and provides for the granting of incentive and non-qualified stock options, restricted stock awards (RSAs), restricted stock units (RSUs), stock appreciation rights, stock bonus awards and performance awards to qualified employees, non-employee directors and consultants. Options granted under the 2014 Plan generally expire within ten years from the date of grant and generally vest over one to four years. Restricted stock units (RSUs) granted under the 2014 Plan generally vest over two to four years based upon continued service and are settled at vesting in shares of the Company’s Class A common stock. Performance stock units (PSUs) granted under the 2014 Plan generally vest over three years based upon continued service and the Company achieving certain financial and operating targets and are settled at vesting in shares of the Company’s Class A common stock. The Company accounts for forfeitures of stock-based payment awards in the period they occur.

The 2014 ESPP allows eligible employees to purchase shares of the Company’s Class A common stock through payroll deductions at a price equal to 85% of the lesser of the fair market value of the stock as of the first date or the ending date of each six-month offering period. The 2014 Plan and the ESPP also provide for automatic annual increases in the number of shares reserved for future issuance.

In June 2023, the Company’s stockholders approved the 2024 Equity Incentive Plan (2024 Plan) and the 2024 Employee Stock Purchase Plan (2024 ESPP) which will be the successors to the Company’s 2014 Plan and 2014 ESPP, respectively. The effective date of both the 2024 Plan and the 2024 ESPP is February 15, 2024. The 2014 Plan and the 2014 ESPP will each expire on February 15, 2024. Awards granted under the 2014 Plan will continue to be subject to the terms and provisions of the 2014 Plan.

Employee retirement plan. The Company has a defined contribution retirement plan covering the United States and other international full-time employees that provides for voluntary employee contributions from 1% to 100% of annual compensation, subject to a maximum limit allowed by Internal Revenue Service guidelines. In certain locations, the Company makes contributions to employee defined contribution plans, these contributions were $0.9 million, $0.8 million, and $0.8 million in 2023, 2022, and 2021, respectively.


	Shares (in thousands)	Weighted-average exercise price		Weighted-average remaining contractual term (in years)	Aggregate intrinsic value (in thousands)
Outstanding at December 31, 2022	3,089	$	9.37	5.30	$	467
Granted	198	3.58
Exercised	—	—
Forfeited/Cancelled	(603)	11.64
Outstanding at December 31, 2023	2,684	$	8.43	5.08	$	—

Vested and expected to vest at December 31, 2023	2,684	$	8.43	5.08	$	—
Exercisable at December 31, 2023	2,250	$	8.92	4.40	$	—

The weighted-average grant date fair value of all options granted was $2.14, $5.05, and $4.62 per share in 2023, 2022, and 2021, respectively. The total fair value of all options vested was $1.4 million, $1.5 million, and $1.5 million in 2023, 2022, and 2021, respectively. The aggregate intrinsic value of the stock options outstanding as of December 31, 2023 represents the value of the Company’s closing stock price on December 31, 2023 in excess of the exercise price multiplied by the number of options outstanding.


	Shares (in thousands)	Weighted-average grant date fair value
Non-vested shares at December 31, 2022	8,727	$	7.19
Granted	8,595	5.13
Vested	(5,224)	6.61
Forfeited	(604)	6.68
Non-vested shares at December 31, 2023	11,494	$	5.94

The weighted-average grant date fair value of all RSUs granted was $5.13, $7.68, and $8.83 per share in 2023, 2022, and 2021, respectively. The total fair value of all RSUs vested was $34.5 million, $30.8 million, and $28.5 million in 2023, 2022, and 2021, respectively.


	Shares (in thousands)	Weighted-average grant date fair value
Non-vested shares at December 31, 2022	686	$	7.93
Granted	1,254	5.79
Vested	(485)	7.71
Forfeited	(631)	5.86
Non-vested shares at December 31, 2023	824	$	6.38

The weighted-average grant date fair value of all PSUs granted was $5.79, $8.70, and $7.93 per share in 2023, 2022, and 2021, respectively. The total fair value of all PSUs vested was $3.7 million, $4.8 million, and $3.0 million in 2023, 2022, and 2021, respectively.

Employee stock purchase plan. For 2023, 2022, and 2021 the Company issued 0.9 million, 0.7 million, and 0.8 million shares under its ESPP, respectively, at weighted-average prices of $4.10, $6.72, and $5.28 per share, respectively.

Fair value disclosures. The Company measures compensation expense for all stock-based payment awards based on the estimated fair values on the date of the grant. The fair value of RSUs and PSUs are determined using the Company’s closing stock price on the date of grant. The Company recognizes compensation expense for PSUs when it is probable that the vesting conditions will be met. The fair value of stock options granted and purchases under the Company’s ESPP are estimated using the Black-Scholes option pricing model. Expected term of stock options granted was estimated based on the simplified method. Expected stock price volatility was estimated by taking the Company’s average historical volatility. Risk-free interest rate was based on the yields of U.S. Treasury securities with maturities similar to the expected term. Dividend yield was zero as the Company does not have any history of, nor plans to make, dividend payments.


	Year ended December 31,
(in thousands)		2023		2022		2021
Cost of revenue		$	1,955	$	1,805	$	1,794
Research and development		19,062		17,221		17,263
Sales and marketing		8,736		8,173		8,045
General and administrative		11,726		11,792		11,548
Total stock-based compensation expense		$	41,479	$	38,991	$	38,650

The income tax benefit related to stock-based compensation expense was $9.3 million, $8.6 million and $9.0 million for the year ended December 31, 2023, 2022, and 2021 respectively. See Note 8, Income taxes, for additional details.

As of December 31, 2023, total unearned stock-based compensation of $57.0 million related to stock options, RSUs, PSUs, and ESPP shares is expected to be recognized over a weighted-average period of 2.24 years.