14. Stock-Based Compensation

The Company maintains the 2021 Equity Incentive Plan (the “2021 Plan”). As of March 31, 2025, 24,276,338 shares remained for future issuance under the 2021 Plan. To date, the Company has issued only stock options and restricted stock units to employees, directors and consultants.

For the three months ended March 31, 2025 and 2024, total stock-based compensation expense was $9.6 million and $9.5 million, respectively. 

Stock Options

The compensation costs for stock option awards are recognized using the straight-line attribution method over the requisite service period and are accounted for forfeitures as they occur. Stock options vest over a four-year service period and expire on the tenth anniversary of the date of award. 

On March 14, 2025, the Company granted 269,685 options under the 2021 Plan. The Company estimated the grant date fair value of these stock options using the Black-Scholes option-pricing model with the following weighted-average assumptions:

To estimate the expected life of stock options, the Company considered the vesting term, contractual expiration period, and market conditions. Expected volatility is based on historical volatility of a group of peer entities. Dividend yields are based upon historical dividend yields. Risk-free interest rates are based on the implied yields currently available on U.S. Treasury zero coupon issues with a remaining term equal to the expected life. Based on these inputs, the grant-date fair value was determined to be $2.2 million.

As of March 31, 2025, there was $7.4 million in unrecognized compensation costs related to all unvested options.

As of  March 31, 2025, the Company had 23,131,333 options outstanding and 21,237,602 options exercisable with intrinsic values of $230.3 million and $218.4 million, respectively. During the three months ended March 31, 2025, 418,369 options were exercised, with a total intrinsic value of $5.9 million.

Restricted Stock Units

Under the terms of the 2021 Plan, we have issued restricted stock unit awards with a continuous employment condition only (“Time-Based RSUs”), and restricted stock unit awards with a continuous employment condition that are also contingent on the Company meeting certain performance goals (“PSUs”, and together “RSUs”). Both types of RSU awards vest over a four-year period from the grant date.

2,041,643 Time-Based RSUs and 301,842 PSUs were granted under the 2021 Plan during the three months ended March 31, 2025, with a weighted-average grant date fair-value of $14.66 per award. The compensation costs for RSUs are recognized using the straight-line attribution method over the requisite service period and are accounted for forfeitures as they occur. RSUs are measured at the fair market value of the underlying stock at the grant date. RSUs that vested during the three months ended  March 31, 2025 had an aggregate fair value at vesting of $26.2 million. As of March 31, 2025, there was $79.5 million in unrecognized compensation costs specific to the unvested RSUs, to be recognized over a weighted-average period of 2.9 years. As of  March 31, 2025, the Company had 9,423,644 unvested Time-Based RSUs and 804,518 unvested PSUs with a weighted-average grant date fair-value of $8.19 per award.