The Company grants stock-based awards under its 2021 Stock Option and Incentive Plan (the “2021 Plan”), which was approved by its stockholders in February 2021 and amended and restated in January 2023. The Company also has outstanding stock

option awards under its 2017 Stock Option and Grant Plan (the “Private Disc Plan”), the 2017 Stock Option and Grant Plan (the “Gemini 2017 Plan”), and the 2021 Inducement Plan, but is no longer granting awards under these plans. The Company also has the option to grant awards under the 2021 ESPP, which was approved by shareholders in July 2021 and amended and restated in January 2023.

The following table summarizes stock option activity for the nine months ended September 30, 2023.


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (In Years)		Aggregate Intrinsic Value (In Thousands)
Outstanding at December 31, 2022		2,640,590		$	16.19		8.08	$	25,513
Granted		181,246			41.48
Exercised		(175,191	)		11.38
Forfeited		(17,684	)		15.00
Expired		(70,430	)		102.56
Outstanding at September 30, 2023		2,558,531		$	15.95		7.77	$	86,191
Exercisable at September 30, 2023		1,285,226		$	16.00		6.84	$	46,219

The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the common stock as of the end of the period. The aggregate intrinsic value of stock options exercised during the nine months ended September 30, 2023 was $4.5 million.

The weighted-average assumptions used to estimate the fair value of stock options granted were as follows:


	Nine Months Ended September 30,
	2023			2022
Risk-free interest rate		3.87	%		2.24	%
Expected term (in years)		7.14			6.00
Expected volatility		59	%		55	%
Expected dividend yield		0	%		0	%
Fair value per share of common stock	$	41.48		$	13.41

The weighted-average grant date fair value of options granted during the nine months ended September 30, 2023 and 2022 was $25.68 and $7.21 per share, respectively.

The total fair value of options vested during the nine months ended September 30, 2023 was $2.9 million.

As of September 30, 2023, the Company had issued a total of 63,061 shares of restricted common stock to the founders of Private Disc pursuant to subscription agreements and to certain key employees pursuant to the Private Disc Plan at $0.0001 per share. The stock restrictions relate to the sale and transferability of the stock and lapse over the defined vesting period in the restricted stock agreement. The vesting period is generally contingent upon continued employment or consulting services being provided to the Company. In the event of termination, the Company has the right, but not the obligation to repurchase the unvested shares at the original purchase price. As of September 30, 2023, all awards of restricted common stock were fully vested.

A summary of restricted common stock activity is as follows:


	Nine Months Ended September 30,
	2023			2022
Unvested at the beginning of the year		1,916			10,170
Vested		(1,916	)		(6,854	)
Unvested at the end of the period		—			3,316

Total stock-based compensation expense recorded as research and development and general and administrative expenses, respectively, for employees, directors and non-employees is as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	455	$	140	$	1,167	$	422
General and administrative		815		242		2,436		674
Total stock-based compensation expense	$	1,270	$	382	$	3,603	$	1,096

As of September 30, 2023, the total unrecognized stock-based compensation expense related to outstanding awards was $11.1 million and is expected to be recognized over a weighted-average period of 2.76 years.