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. The 2019 Plan was terminated as of the close of the Merger, and no shares remain available for future issuance under the 2019 Plan. Any options outstanding under the 2019 Plan remained outstanding and effective.

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.

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 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. On June 18, 2024, the Company’s stockholders approved the amendment and restatement of the 2020 Plan, which increased the number of shares authorized for issuance thereunder by 2,900,000 shares. As of June 30, 2024, 4,140,001 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.

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 “ESPP”), which became effective on March 11, 2020. The 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. Purchase dates under the ESPP occur on or about June 13 and December 13 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 Reverse Stock Split effected on February 23, 2023, the number of shares reserved for issuance under the 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 June 30, 2024, 778,089 shares of the Company’s common stock remained available for issuance under the ESPP.

The Company issued 31,801 and 0 shares under the ESPP during the six months ended June 30, 2024 and 2023, respectively. The Company had an outstanding liability of $67,000 and $53,000 at June 30, 2024 and December 31, 2023, respectively, which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets, for employee contributions to the ESPP for shares pending issuance at the end of the offering period. As of June 30, 2024, total stock-based compensation cost not yet recognized related to stock purchase rights under the ESPP was $0.1 million, which is expected to be recognized over a weighted-average period of 0.5 years.

The following table summarizes stock option activity:


	Stock Options Outstanding			Weighted-Average Exercise Price
Outstanding - January 1, 2024		5,817,339		$	11.90
Options granted		2,178,094			15.04
Options exercised and vested		(524,502	)		4.42
Options cancelled and forfeited		(6,180	)		18.60
Outstanding - June 30, 2024		7,464,751		$	13.34

As of June 30, 2024, total compensation cost not yet recognized related to unvested stock options was $49.2 million, which is expected to be recognized over a weighted-average period of 2.8 years.

Upon formation of Former Enliven in June 2019, Former Enliven issued approximately 3.0 million shares in restricted common stock to its founders. Additionally, between 2019 and 2020, Former Enliven issued a total of 197,262 shares of restricted stock to employees and consultants. As of June 30, 2024, total compensation cost not yet recognized for restricted stock awards was immaterial.

Restricted stock units ("RSUs") are valued at the market price of a share of the Company’s common stock on the date of grant. The following table summarizes RSU activity:


	Number of Shares			Weighted-Average Grant Date Fair Value
Unvested - January 1, 2024		78,505		$	14.28
Granted		20,000			14.85
Vested		(4,437	)		18.82
Forfeited		—			—
Unvested - June 30, 2024		94,068		$	14.19

As of June 30, 2024, total compensation cost not yet recognized related to unvested RSUs was $1.2 million, which is expected to be recognized over a weighted-average period of 3.3 years.

The allocation of stock-based compensation expense was as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Research and development	$	2,528	$	2,210	$	4,757	$	2,702
General and administrative		2,616		1,985		4,902		3,755
Total stock-based compensation expense	$	5,144	$	4,195	$	9,659	$	6,457

The assumptions used in the Black-Scholes model to determine the fair value of stock option grants and stock purchase rights under the ESPP were as follows:


	Six Months Ended June 30,
Stock Options	2024	2023
Expected term (years)	5.7 - 6.1	5.8 - 6.0
Expected volatility	82% - 84%	83% - 84%
Risk-free interest rate	4.0% - 4.6%	3.3% - 4.1%
Expected dividend yield	—%	—%


	Six Months Ended June 30,
ESPP	2024	2023
Expected term (years)	0.5	N/A
Expected volatility	75%	N/A
Risk-free interest rate	5.4%	N/A
Expected dividend yield	—%	N/A