In September 2009, the Company’s board of directors approved the 2009 Stock Incentive Plan (the “2009 Plan”) which provided for the grant of incentive stock options to employees and non-statutory stock options to directors, consultants, and non-employees of the Company. The 2009 Plan terminated in July 2019 effective upon the completion of the Company’s IPO. No additional options will be granted under the 2009 Plan. As of March 31, 2023, there were 2,112,180 options outstanding under the 2009 Plan.

In May 2019, the Company’s board of directors approved the 2019 Stock Option and Incentive Plan (the “2019 Plan”) which became effective on June 26, 2019, the date immediately prior to the date on which the registration statement related to the IPO was declared effective by the SEC. The 2019 Plan will expire in May 2029. Under the 2019 Plan, the Company may grant incentive stock options, non-statutory stock options, restricted stock awards, RSUs, and other stock-based awards. There were 1,709,832 shares of the Company’s common stock initially reserved for issuance under the 2019 Plan. The number of shares of common stock underlying awards that expire, or are terminated, surrendered, canceled or forfeited without having been fully exercised under the 2009 Plan will be added to the shares of common stock available for issuance under the 2019 Plan. In addition, the number of shares of common stock that may be issued under the 2019 Plan automatically increases on January 1 of each calendar year, commencing on January 1, 2020, by 4% of the number of shares of common stock outstanding on the immediately preceding December 31 or such lesser amount determined by the Company’s board of directors or the compensation committee of the board of directors. As of March 31, 2023, there were 2,628,784 common shares available for issuance, 3,697,803 options outstanding, and 209,433 RSUs outstanding under the 2019 Plan.

Option awards under the 2019 Plan generally vest based on the grantee’s continued service with the Company during a specified period following a grant and expire ten years from the grant date. Awards typically vest in four years, but vesting conditions can vary based on the discretion of the Company’s board of directors.

A summary of the Company’s stock option activity and related information is as follows:


	Number of Shares			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022		5,570,355		$	63.82		7.2	$	744,097
Granted		404,098			191.49
Exercised		(72,815	)		76.47
Forfeited		(91,655	)		150.19
Outstanding as of March 31, 2023		5,809,983		$	71.18		7.1	$	652,227
Options vested and expected to vest as of March 31, 2023		5,809,983		$	71.18		7.1	$	652,227
Options exercisable as of March 31, 2023		3,836,456		$	36.72		6.3	$	555,962

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the publicly traded stock price of the Company’s common stock as of March 31, 2023.

As of March 31, 2023, there was $149.0 million of unrecognized compensation cost, which is expected to be recognized over a weighted-average period of 2.9 years.

The weighted-average fair values of options granted during the three months ended March 31, 2023 and 2022 was $113.45 and $67.49, respectively. The intrinsic value of options exercised during the three months ended March 31, 2023 and 2022 was $8.4 million and $5.8 million, respectively.

RSUs are granted to certain employees and are payable in shares of our common stock. RSU shares are accounted for at fair value based upon the closing stock price on the date of grant. The corresponding expense is amortized over the vesting period, which is typically four years.

A summary of the Company’s restricted stock unit activity and related information is as follows:


	Number of Shares			Weighted- Average Grant Date Fair Value
Unvested as of December 31, 2022		—		$	—
Granted		210,748			191.54
Vested		—			—
Forfeited		(1,315	)		191.79
Unvested as of March 31, 2023		209,433		$	191.54

As of March 31, 2023, the total remaining unrecognized compensation cost related to nonvested RSUs was $38.6 million, which will be amortized over the weighted-average remaining requisite service period of 3.9 years.

Stock-based compensation expense is classified in the statements of operations for the three months ended March 31, 2023 and 2022 as follows (in thousands):


	Three Months Ended March 31,
	2023		2022
Research and development	$	8,835	$	4,530
General and administrative		6,672		6,106
Total stock-based compensation expense	$	15,507	$	10,636