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Stock-Based Compensation
 3 Months Ended
Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Stock-Based Compensation Stock-Based Compensation
The Company measures stock-based awards at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company recorded stock-based compensation expense in the following expense categories in its accompanying statements of operations (in thousands):
Three Months Ended
March 31,
20242023
Research and development$564 $174 
General and administrative481 119 
Total expense$1,045 $293 

The following table summarizes the option activity:
Number
of
shares		Weighted
average
exercise price
per share
Weighted
average
remaining
contractual
term
(years)
Outstanding at December 31, 2023823,833$31.43 5.89
Granted741,652 $34.59 
Exercised(37,330)$16.89 
Expired/Forfeited(52,697)$72.62 
Outstanding at March 31, 20241,475,458$31.03 7.77
Exercisable at March 31, 2024530,779 $30.95 5.15
As of March 31, 2024, the aggregate intrinsic value of outstanding options and exercisable options was approximately $32.2 million and $15.1 million, respectively. The aggregate intrinsic value of options exercised was approximately $0.7 million for the three months ended March 31, 2024.
The weighted-average grant date fair value of options granted was $25.97 and $12.99 per share for the three months ended March 31, 2024 and 2023, respectively. The Company recorded stock-based compensation related to stock options of approximately $1.0 million and $0.3 million for the three months ended March 31, 2024 and 2023, respectively. As of March 31, 2024, the total unrecognized compensation expense related to unvested stock option awards was approximately $18.7 million, which the Company expects to recognize over a weighted-average period of 3.43 years.
The fair value of each option was estimated on the grant date using the weighted average assumptions in the table below:
Three Months Ended
March 31,
20242023
Expected volatility
86.39%-87.64%
82.96%-83.70%
Risk-free interest rate
3.97%-4.32%
3.45%-4.46%
Expected life (in years)
5.77-6.08
3.58-6.08
Expected dividend yield— — 
Fair value of common stock (1)
$18.39 
(1) Prior to the reverse merger, the Company periodically estimated the fair value of the Company’s common stock considering, among other things, valuations of its common stock prepared by management with the assistance of a third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants 2013 Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. Following the reverse merger, the fair value of the Company’s common stock is based on the closing stock price on the date of grant as reported on the Nasdaq Global Market.

A summary of the Company’s RSU activity and related information for the three months ended March 31, 2024 is as follows:
Number of SharesWeighted Average Grant Date Fair Value
Unvested at December 31, 2023— $— 
Restricted stock units granted482,384 $36.06 
Unvested at March 31, 2024482,384 $36.06 
252,124 of these RSUs were granted with vesting in two equal tranches based on certain performance conditions ("PSUs"). Each PSU entitles the holder to receive one share of the Company's common stock when the PSU vests. During the three months ended March 31, 2024, the related performance conditions were not met and are not currently considered probable to vest. As such, no expense is recognized as of March 31, 2024.
The Company recorded stock-based compensation expense related to RSUs of approximately $0.1 million for the three months ended March 31, 2024. As of March 31, 2024, there was approximately $8.2 million of unrecognized compensation cost related to unvested RSUs, which is expected to be recognized over a remaining weighted average vesting period of approximately 2.95 years.