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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Stock Option Valuation The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted:


Year Ended
December 31,



2024

20232022
Risk-free interest rate


4.1 %

4.1 %3.4 %
Expected term (in years)


6.1

6.06.1
Expected volatility


98.3 %

93.9 %96.0 %
Expected dividend yield


— %

— %— %
Summary of Stock Option Activity
The following table summarizes the Company’s stock option activity for the twelve months ended December 31, 2024:

Number of
Shares

Weighted
Average
Exercise
Price

Weighted
Average
Contractual
Term
(in Years)

Aggregate Intrinsic
Value
(in Thousands)
Outstanding as of December 31, 20236,008,541 

$2.97 

8.6

$24 
Granted6,920,932 

0.92 




Forfeited(1,085,977)

1.56 



$1 
Outstanding as of December 31, 202411,843,496 

$1.90 

8.6

$269 
Exercisable as of December 31, 20242,851,579 

$4.63 

6.8

$— 
Vested and expected to vest as of December 31, 20249,730,725 

$2.09 

8.4

$200 
Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity
The following table summarizes the Company’s restricted stock activity for the twelve months ended December 31, 2024 :
Number of SharesWeighted Average Grant Date Fair Value
Unvested at December 31, 20233,118,824 $1.61 
Granted6,292,459 $0.95 
Vested(2,876,806)$1.64 
Forfeited(532,652)$0.97 
Unvested at December 31, 20246,001,825 $0.96 
Summary of Stock-Based Compensation Expense Classification
Stock-based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows:

Year Ended
December 31,
(in thousands)
2024

20232022
Research and development expense$4,291 

$4,357 $2,534 
Selling, general and administrative expense3,913 

4,330 2,665 
Total stock-based compensation$8,204 

$8,687 $5,199 
Schedule of Stock Appreciation Right Assumptions and Activity
The calculation of the fair value of the outstanding SARs includes the closing price of the Company’s common stock of $0.73 and $0.84 as of December 31, 2024 and December 31, 2023, respectively, and the following assumptions on a weighted average basis:
December 31,
2024		December 31,
2023		December 31,
2022
Common stock price$0.73 $0.84 $0.99 
Risk-free interest rate4.3 %3.8 %4.0 %
Expected term (in years)3.894.865.86
Expected volatility112.7 %100.0 %97.0 %
Expected dividend yield— %— %— %
Expected forfeiture rate6.2 %18.6 %22.3 %
The following table summarizes the Company’s SARS activity for the twelve months ended December 31, 2024 :

Number of
Shares

Outstanding as of December 31, 20237,138,335 

Granted3,273,718 

Outstanding as of December 31, 202410,412,053 

Vested as of December 31, 20244,092,224 

The weighted average grant-date fair value per share of SARs granted during the years ended December 31, 2024 and December 31, 2022 was $0.92 and $0.71 per share, respectively. There were no grants of SARs for the year ended December 31, 2023.