Share-based compensation expense recorded in the accompanying condensed statements of operations is as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Research and development expense	$	4,709	$	3,410	$	9,362	$	6,790
Selling, general and administrative expense		8,321		6,067		16,312		12,134
Total share-based compensation expense	$	13,030	$	9,477	$	25,674	$	18,924

In October 2022, the board of directors and stockholders approved the 2022 Equity Inducement Plan, or the 2022 Plan. The 2022 Plan provides for the grant of non-statutory stock options and restricted stock units. The number of shares of common stock reserved for issuance under the 2022 Plan is 1,000,000 shares.

In May 2021, in connection with the IPO, the board of directors and stockholders approved, the 2021 Equity Incentive Plan, or the 2021 Plan, which became effective on the day before the date of the effectiveness of the IPO. The 2021 Plan provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, awards of restricted stock, restricted stock units and other share-based awards. The number of shares of common stock reserved for issuance under the 2021 Plan is equal to the sum of: (x) 6,369,000 shares of common stock; plus (y) 4,719,605 shares of common stock issued in respect of the conversion of incentive shares that were subject to vesting immediately prior to the effectiveness of the registration statement for the IPO that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right. The number of shares available for grant and issuance under the 2021 Plan will be automatically increased on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including, the fiscal year commencing on January 1, 2031, by the lesser of (a) 5% of the number of shares of all classes of the Company’s common stock, plus the total number of shares of Company common stock issuable upon conversion of any preferred stock or exercise of any warrants to acquire shares of Company common stock for a nominal exercise price issued and outstanding on each December 31 immediately prior to the date of increase or (b) such number of shares determined by the board of directors.

The following table provides a summary of stock option activity during the six months ended June 30, 2024.


	Options			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2023		10,211,758		$	17.10
Granted		2,597,862		$	14.36
Exercised		(27,013	)	$	13.76			$	68
Forfeiture		(578,985	)	$	16.89
Outstanding at June 30, 2024		12,203,622		$	16.54		7.9	$	2,237
Vested and expected to vest at June 30, 2024		12,203,622		$	16.54		7.9	$	2,237
Exercisable at June 30, 2024		6,400,855		$	16.68		7.3	$	1,011

Aggregate intrinsic value represents the difference between the estimated fair value of the underlying common stock and the exercise price of outstanding, in-the-money options. The total intrinsic value of options exercised during the six months ended June 30, 2024 and 2023 was less than $0.1 million and $0.6 million, respectively.

The total fair value of options that vested during the six months ended June 30, 2024 and 2023 was $17.9 million and $12.8 million, respectively. The weighted-average grant date fair value of options granted during the six months ended June 30, 2024 and 2023 was $9.26 per share and $13.81 per share, respectively.

Unamortized share-based compensation for stock options as of June 30, 2024 was $59.6 million, which is expected to be recognized over a weighted-average period of 2.4 years.

The Company used the Black-Scholes option pricing model to estimate the fair value of stock option awards granted with the following assumptions:


	Three Months Ended June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Expected term (in years)	5.3 - 6.1	5.3 - 6.2	5.3 - 6.7	5.3 - 6.3
Expected volatility	68.57% - 69.18%	69.21% - 81.65%	68.27% - 70.57%	69.21% - 81.98%
Risk-free interest rate	4.24% - 4.47%	3.47% - 3.98%	3.90% - 4.47%	3.47% - 4.08%
Expected dividend yield	—	—	—	—

The following table provides a summary of restricted stock units activity during the six months ended June 30, 2024:


	Number of Shares			Weighted Average Grant Date Fair Value Per Share
Unvested restricted stock units at December 31, 2023		1,031,545		$	18.27
Granted		1,430,880		$	14.45
Vested		(369,359	)	$	16.63
Forfeiture		(176,478	)	$	16.41
Unvested restricted stock units at June 30, 2024		1,916,588		$	15.90

Unamortized share-based compensation for restricted stock units as of June 30, 2024 was $28.7 million, which is expected to be recognized over a weighted-average period of 3.0 years.

The following table provides a summary of the unvested common stock awards activity during the six months ended June 30, 2024.


	Number of Shares			Weighted Average Grant Date Fair Value Per Share
Unvested common stock as of December 31, 2023		747,679		$	16.00
Vested		(376,591	)	$	16.00
Forfeiture		(25,415	)	$	16.00
Unvested common stock as of June 30, 2024		345,673		$	16.00

Unamortized share-based compensation for restricted stock awards as of June 30, 2024 was $1.9 million, which is expected to be recognized over a weighted-average period of 0.7 years.

In May 2021, the board of directors adopted and the stockholders approved the 2021 Employee Stock Purchase Plan, or the ESPP, which became effective on May 26, 2021. A total of 603,000 shares of common stock were initially reserved for issuance under the ESPP. The number of shares of the common stock reserved for issuance under the ESPP will automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including, the fiscal year commencing on January 1, 2031, by the lesser of: (a) 1% of the total number of outstanding shares of common stock of the Company (on an as converted basis outstanding on the immediately preceding December 31 (rounded down to the nearest whole share)) and (b) an amount determined by the board of directors. 331,014 shares have been issued under the ESPP as of June 30, 2024. The Company recognized compensation expense related to the ESPP of $0.2 million and $0.3 million for the three months ended June 30, 2024 and 2023, respectively, and $0.4 million and $0.5 million for the six months ended June 30, 2024 and 2023, respectively.

The fair value of our common stock to be issued under the ESPP is estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Six Months Ended June 30,
	2024	2023
Expected term (in years)	0.5	0.5
Expected volatility	63.45%	63.57%
Risk-free interest rate	5.40%	5.24%
Expected dividend yield	—	—