Stock-Based Compensation | 11. Stock-Based Compensation Equity Incentive Plans 2019 Equity Incentive Plan In July 2019, Former Enliven adopted the 2019 Equity Incentive Plan (the “2019 Plan”) pursuant to which its board of directors may grant non-statutory stock options, stock appreciation rights, restricted stock, and restricted stock units to employees and non-employees and incentive stock options only to employees. After giving effect to the exchange ratio, the 2019 Plan initially authorized grants of awards of up to 374,076 shares of Former Enliven’s common stock. In April 2020, the board of directors increased the number of shares of Former Enliven’s common stock authorized for issuance under the 2019 Plan by 2,210,062 to 2,584,138 shares. Additionally, in December 2020, the board of directors approved an increase in the number of shares of Former Enliven’s common stock authorized for issuance under the 2019 Plan by 1,211,791 to 3,795,929 shares. In August 2022, the board of directors approved an increase in the shares authorized under the 2019 Plan of 885,315 shares, for a total authorized amount of 4,681,244 . The 2019 Plan was terminated as of the consummation of the business combination between Former Enliven and the Company, and no shares remain available for future issuance under the 2019 Plan. Any options outstanding under the 2019 Plan remained outstanding and effective. 2016 Stock Incentive Plan The Company’s 2016 Stock Incentive Plan, (the “2016 Plan”) provided for the grant of restricted stock, restricted stock units, stock appreciation rights, incentive stock options, non-statutory stock options and other stock-based awards to employees, officers, members of the board of directors, consultants and advisors of the Company. As of the effective date of the 2020 Equity Incentive Plan, no shares remained available for future issuance under the 2016 Plan. Any options or awards outstanding under the 2016 Plan remained outstanding and effective. 2020 Equity Incentive Plan On October 1, 2019, the Company’s board of directors adopted, and on February 26, 2020 the Company’s stockholders approved, the 2020 Equity Incentive Plan, which became effective on March 11, 2020 (the “2020 Plan”). The 2020 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. On November 8, 2022, the Company’s board of directors adopted, and on February 22, 2023, the Company’s stockholders approved, the amendment and restatement of the 2020 Plan. Following the 1-to- 4 reverse stock split effected on February 23, 2023, the number of shares reserved for issuance under the 2020 Plan is equal to 4,275,000 shares of the Company’s common stock. The number of shares reserved shall be annually increased on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2024 and continuing until, and including, the fiscal year commencing January 1, 2032, equal to the least of (i) 4.5 % of the number of shares of the Company’s common stock outstanding on the first day of such fiscal year and (ii) an amount determined by the Company’s board of directors. The shares of common stock underlying any awards that expire, terminate, or are otherwise surrendered, cancelled, forfeited or repurchased by the Company under the 2020 Plan will be added back to the shares of common stock available for issuance under the 2020 Plan. As of March 31, 2023, 3,829,005 shares of the Company’s common stock remained available for issuance under the 2020 Plan. Awards granted under the Company’s equity plans expire no later than 10 years from the date of grant. Options and restricted stock granted to employees typically vest over a four-year period but may have been granted with different vesting terms. 2020 Employee Stock Purchase Plan On October 1, 2019, the Company’s board of directors adopted, and on February 26, 2020, the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective on March 11, 2020. The 2020 ESPP permits eligible employees who elect to participate, in six-month offering periods, to purchase shares of common stock through payroll deductions at a price equal to 85 % of the fair market value of the common stock on the first or last business day of each applicable six-month offering period, whichever is lower. Prior to the business combination between the Former Enliven and the Company, purchase dates under the ESPP occurred on or about June 14 and December 14 each year. On November 8, 2022, the Company’s board of directors adopted, and on February 22, 2023, the Company’s stockholders approved, an amendment to the ESPP to increase its share reserve. Following the 1-to- 4 reverse stock split effected on February 23, 2023, the number of shares reserved for issuance under the 2020 ESPP is equal to 407,133 shares of the Company’s common stock. The number of shares reserved shall be annually increased on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2024 and continuing until, and including, the fiscal year commencing January 1, 2043, equal to the least of (i) 407,133 shares of the Company’s common stock, (ii) 1 % of the number of shares of the Company’s common stock outstanding on the first day of such fiscal year and (iii) an amount determined by the Company’s board of directors. As of March 31, 2023, 402,757 shares of the Company’s common stock remained available for issuance under the 2020 ESPP. Stock Option Repricing Effective August 9, 2022, the Former Enliven’s board of directors repriced certain previously granted and still outstanding vested and unvested stock option awards under the 2019 Plan. As a result, the exercise price for these awards was lowered to $ 2.48 per share, which was the fair value of the Former Enliven’s common stock on August 9, 2022. No other terms of the repriced stock options were modified, and the repriced stock options will continue to vest according to their original vesting schedules and will retain their original expiration dates. As a result of the repricing, 2,209,826 vested and unvested stock options outstanding as of August 9, 2022, with original exercise prices ranging from $ 4.68 to $ 7.56 , were repriced. The repricing on August 9, 2022 resulted in incremental stock-based compensation expense of $ 1.0 million, of which $ 0.3 million related to vested stock option awards and was expensed on the repricing date, and $ 0.7 million related to unvested stock option awards is being amortized on a straight-line basis over the remaining weighted-average vesting period of those awards of 2.9 years. The following table summarizes the stock plan activity: Stock Options Weighted-Average Outstanding - January 1, 2023 3,316,671 $ 2.20 Assumption of options in connection with the Merger 449,900 28.40 Options granted 199,860 25.28 Options exercised and vested ( 76,165 ) 2.79 Options cancelled and forfeited — — Outstanding - March 31, 2023 3,890,266 $ 7.58 The Company records stock-based compensation expense on a straight-line basis over the vesting period. As of March 31, 2023, total compensation cost not yet recognized related to unvested stock options was $ 11.1 million, which is expected to be recognized over a weighted-average period of 2.4 years. Restricted stock award activity Upon formation of Former Enliven in June 2019, Former Enliven issued approximately 3.0 million shares in restricted common stock to its founders at approximately $ 0.0003 per share. 25 % of the shares vested immediately upon issuance, with the remaining shares vesting evenly over 36 or 48 months. Vesting may be accelerated upon a change in control, as defined in the holder agreements. If the holders cease to have a business relationship with the Company, any unvested shares held by these individuals may be repurchased at their original purchase price. The unvested restricted stock is not considered outstanding for accounting purposes until the shares vest. As of March 31, 2023 and December 31, 2022, there were 20,749 and 41,499 shares subject to repurchase, respectively. Additionally, between 2019 and 2020, Former Enliven issued a total of 197,262 shares of restricted stock to employees and consultants for aggregate consideration of $ 27,000 . The purchase price of the restricted stock was the estimated fair value on the grant date. The restricted stock awards are subject to vesting over a period of four to five years , and vesting may be accelerated upon a change in control, as defined in the holder agreements. If the holders cease to have a business relationship with the Company, any unvested shares held by these individuals may be repurchased at their original purchase price. The unvested restricted stock is not considered outstanding for accounting purposes until the shares vest. The following summarizes restricted stock activity: Number of Shares Weighted-Average Grant Date Fair Value Unvested - January 1, 2023 50,457 $ 0.14 Granted — — Vested ( 11,867 ) 0.14 Forfeited — — Unvested - March 31, 2023 38,590 $ 0.14 As of March 31, 2023, total compensation cost not yet recognized was immaterial. Stock-based compensation expense The allocation of stock-based compensation expense was as follows (in thousands): Three Months Ended March 31, 2023 2022 Research and development 492 349 General and administrative 1,770 305 Total stock-based compensation expense $ 2,262 $ 654 The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes model. The following summarizes the inputs used: Three Months Ended March 31, 2023 2022 Stock Price $ 25.28 $ 6.78 Expected term (years) 5.8 6.0 - 6.3 Expected volatility 83 % 80 % Risk-free interest rate 4.1 % 1.6 % - 2.0 % Expected dividend yield — — |