On December 28, 2015, the Company’s board of directors adopted the C4 Therapeutics, Inc. 2015 Incentive Stock Option and Grant Plan (the “2015 Plan”) and reserved 2,525,327 shares of common stock for issuance under this plan. As of April 2019, the shares reserved increased to 3,614,753. On June 3, 2020, the number of shares reserved for issuance under the 2015 Plan was increased to 5,058,203. As of September 30, 2020, 2,364,975 shares remained available for future grant under the 2015 Plan. Following the IPO, no further awards will be granted under the 2015 Plan, though this plan does remain in effect as to previously granted awards.

The 2015 Plan authorizes the board of directors or a committee of the board of directors to grant incentive stock options, nonqualified stock options and restricted stock awards to eligible employees, outside directors and consultants of the Company. Options generally vest over a period of five or eight years, with a cliff vesting at one year and quarterly vesting thereafter and options that lapse or are forfeited are available to be granted again. The contractual life of all options is generally ten years from the date of grant.

In connection with the issuance of stock options, the Company recorded stock-based compensation expense of $0.4 million and $0.6 million for the three months ended September 30, 2020 and 2019, respectively and $0.7 million and $0.9 million for the nine months ended September 30, 2020 and 2019, respectively.

Stock-based compensation expense for the three and nine months ended September 30, 2020 and 2019 was classified in the Company’s condensed consolidated statement of operations and comprehensive loss as follows (in thousands):

	THREE MONTHS ENDED SEPTEMBER 30,				NINE MONTHS ENDED SEPTEMBER 30,
	2020		2019		2020		2019
Research and development	$	345	$	118	$	620	$	272
General and administrative		91		509		93		641
Total stock-based compensation expense	$	436	$	627	$	713	$	913

	NUMBER OF OPTIONS			WEIGHTED- AVERAGE EXERCISE PRICE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL TERM (IN YEARS)		AGGREGATE INTRINSIC VALUE
Outstanding as of December 31, 2019		2,368,950		$	4.35		8.11	$	10,309
Granted		1,467,424			4.98
Exercised		(251,466	)		3.17				2,442
Cancelled or forfeited		(1,229,054	)		4.52
Outstanding as of September 30, 2020		2,355,854			4.82		8.89	$	11,367
Options exercisable as of December 31, 2019		733,310			3.40		7.41	$	2,275
Options exercisable as of September 30, 2020		365,732			4.04		7.28	$	6,949

On March 3, 2020 (“Separation Date”), the employment of the Company’s then current president and chief executive officer (“CEO”) terminated. The Company repurchased all of the CEO’s outstanding shares of common stock, which had been issued upon his exercise of previously granted stock options, for total consideration of $0.1 million. The CEO also relinquished his right to purchase shares of common stock upon the exercise of stock options that were vested as of his termination date, in exchange for total consideration paid by the Company of $0.8 million. The Company recorded the repurchase liability once the termination was deemed probable on March 3, 2020. The Company recognized the repurchase price of these shares of common stock and the relinquishment of these vested options in additional-paid-in-capital.

On September 8, 2020, the Company’s board of directors adopted the C4 Therapeutics, Inc. 2020 Stock Option and Incentive Plan (the “2020 Plan”), which became effective on September 30, 2020. There are 6,567,144 shares of common stock reserved for issuance under the 2020 Plan. Under the 2020 Plan, the compensation committee of the Company’s board of directors (or its designee) is authorized to grant a broad range of equity-based awards, including stock options, stock appreciation rights (“SARs”), restricted stock awards (“RSAs”), restricted stock units (“RSUs”), performance awards and stock bonus awards to the Company’s officers, employees, directors and other key persons, including consultants.

Following the effectiveness of the 2020 Plan, the Company ceased making grants under the 2015 Plan. However, the 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. Shares of common stock subject to awards granted under the 2015 Plan that cease to be subject to such awards by forfeiture or otherwise after the termination of the 2015 Plan will be available for issuance under the 2020 Plan. As of September 30, 2020, no awards had been made under the 2020 Plan.

On September 8, 2020, the Company’s board of directors adopted the C4 Therapeutics, Inc. 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective on September 30, 2020 for use by the Company following the IPO. There are 437,809 shares of common stock reserved for issuance under the 2020 ESPP. All employees meeting eligibility requirements defined in the plan may participate in the 2020 ESPP by purchasing shares of the Company’s common stock. To participate in the 2020 ESPP, eligible employees will authorize payroll deductions of up to 15% of their eligible compensation during an offering period. The Company may hold one of more offering periods each year during which employees will be able to purchase shares under the 2020 ESPP. As of September 30, 2020, the Company had not held any offering periods and no shares had been issued under the 2020 ESPP.