In January 2023, the number of shares of common stock available for issuance under the Company's 2015 Omnibus Incentive Plan, or the 2015 Plan, was increased by 2,724,455 shares due to the automatic annual provision to increase shares available under the 2015 Plan. As of September 30, 2023, the total number of shares of common stock available for issuance under the 2015 Plan was 2,488,979. The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the Company's 2015 Employee Stock Purchase Plan, or ESPP, in the condensed consolidated statements of comprehensive loss as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022

Research and development	$	3,853	$	1,820	$	10,329	$	4,531
General and administrative		4,468		2,542		12,295		7,247
Total	$	8,321	$	4,362	$	22,624	$	11,778

Compensation expense by type of award in the three and nine months ended September 30, 2023 and 2022 was as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022

Stock options	$	7,242	$	3,864	$	19,654	$	9,977
Restricted Stock Units		990		452		2,749		1,690
Employee Stock Purchase Plan		89		46		221		111
Total	$	8,321	$	4,362	$	22,624	$	11,778

During the nine months ended September 30, 2023, the Company granted 3,336,941 stock options to certain executives, consultants and employees having service-based vesting conditions. The grant date fair value of the options granted in the nine months ended September 30, 2023, was $57.1 million, or $17.11 per share on a weighted-average basis and will be recognized as compensation expense over the requisite service period of two to four years.

In February 2022, the Company granted to certain employees 140,000 performance-based stock options, or the 2022 Performance Awards, related to the achievement of certain clinical and regulatory development milestones and market-based conditions. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones.

In the first quarter of 2022, management estimated one of the milestones for the 2022 Performance Awards was probable of achievement and, as such, the Company recorded approximately $258,000 and $346,000 of stock compensation expense for these awards for the nine months ended September 30, 2023 and 2022, respectively. As of September 30, 2023, 140,000 stock options outstanding were unvested, and no options had been canceled.

During the nine months ended September 30, 2023, 628,253 options were exercised for cash proceeds of approximately $5.0 million. During the nine months ended September 30, 2022, 1,167,295 options were exercised for cash proceeds of $10.1 million.

RSUs awarded to members of the Company's board of directors or employees vest on either (i) the one-year anniversary date of the related grant or (ii) 25% on each anniversary date of the related grant for four years. The following table summarizes the Company's RSU activity:



	Number of Shares			Weighted Average Grant Date Fair Value
Unvested—December 31, 2022		224,788		$	18.02
Granted (1)		308,550		$	24.94
Vested		(9,102	)	$	13.87
Unvested—September 30, 2023 (2)		524,236		$	22.16

(1) RSUs granted in 2023 and 2022 had a weighted average grant date fair value of $24.94 and $15.79, respectively. The fair values of RSUs vested in 2023 and 2022 totaled $127,000 and $656,000, respectively.

(2) Unvested RSUs as of September 30, 2023, include 317,333 RSUs which were granted to members of the Company's board of directors and will not be considered issued and outstanding until the occurrence of a separation from service, death, disability, or a change in control.

As of September 30, 2023, there were $82.7 million of unrecognized compensation costs related to employee and non-employee unvested stock options and RSUs granted under the 2015 Plan and 2007 Plan, which are expected to be recognized over a weighted-average remaining service period of 2.9 years.