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Stock Based Compensation
12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Stock Based Compensation

7. Stock-Based Compensation

2021 Equity Incentive Plan

The 2021 Equity Incentive Plan (the 2021 Plan) was approved by the Company’s Board on April 22, 2021 and became effective immediately, although no awards were permitted to be granted under the 2021 Plan until July 15, 2021. The 2021 Plan replaced the 2018 Plan, however, awards outstanding under the 2018 Plan continue to be governed by their existing terms. In addition, shares of common stock subject to awards granted under the 2018 Plan that cease to be subject to such awards by forfeiture or otherwise after the termination of the 2018 Plan will be available for issuance under the 2021 Plan.

There were 3,278,048 shares of common stock initially reserved for issuance under the 2021 Plan and as of December 31, 2023, there were 4,523,924 shares of common stock available for issuance. The number of shares reserved for issuance under the 2021 Plan will be increased automatically on the first business day of each fiscal year, commencing in 2022 and ending in 2031. The aggregate number of common shares that may be issued under the 2021 Plan shall automatically increase by a number equal to the least of (a) 4%

of the total number of shares of common stock actually issued and outstanding on the last day of the preceding fiscal year, or (b) a number of shares common stock determined by the Company’s Board.

2021 Employee Stock Purchase Plan

The 2021 Employee Stock Purchase Plan (the "2021 ESPP") was approved by the Company’s Board on April 22, 2021 and became effective immediately, although no awards were permitted to be granted under the 2021 Plan until July 15, 2021. A total of 254,390 shares of common stock were initially reserved for issuance under the 2021 ESPP. As of December 31, 2023 and 2022, there were 146,380 shares issued under the 2021 ESPP. As of December 31, 2023, there were 589,344 shares of common stock available for issuance under the 2021 ESPP. The number of shares reserved for issuance will automatically be increased on the first business day of each fiscal year, commencing on January 1, 2022 and ending on January 1, 2041. The aggregate number of shares of common stock that may be issued under the 2021 ESPP shall automatically increase by a number equal to the least of (i) one percent (1%) of the total number of shares of common stock actually issued and outstanding on the last day of the preceding fiscal year, or (ii) a number of shares of common stock determined by the Company’s Board.

Stock Compensation

Stock-based compensation expense related to stock options and the stock purchase plan for the years ended December 31, 2023 and 2022 was classified in the consolidated statement of operations as follows (in thousands):

 

 

 

Year Ended
December 31,

 

 

 

2023

 

 

2022

 

Research and development

 

$

2,876

 

 

$

1,626

 

General and administrative

 

 

2,332

 

 

 

2,925

 

Total stock-based compensation expense

 

$

5,208

 

 

$

4,551

 

Stock Options

The Company typically grants stock options at exercise prices deemed by the Board to be equal to the fair value of the common stock at the time of grant, based upon the quoted price of the Company’s common stock.
 

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model. The Company lacks sufficient company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.
 

The weighted-average for each of the assumptions the Company used to determine the grant-date fair value of options granted were as follows:

 

 

 

Year Ended December 31,

 

 

 

2023

 

 

2022

 

Risk free interest rate

 

 

3.95

%

 

 

2.40

%

Expected term (in years)

 

 

6.36

 

 

 

6.24

 

Expected dividend yield

 

 

0

%

 

 

0

%

Expected volatility of underlying common stock

 

 

87

%

 

 

81

%

 

The following table summarizes the stock option activity:

 

 

 

Stock
Options

 

 

Weighted
Average
Exercise
Price

 

 

Weighted
Average
Remaining
Life
(in Years)

 

 

Intrinsic
Value
(in
thousands)

 

Outstanding January 1, 2023

 

 

5,230,537

 

 

$

5.35

 

 

 

8.49

 

 

$

 

Granted

 

 

8,544,660

 

 

 

2.70

 

 

 

 

 

 

 

Exercised

 

 

(316,441

)

 

 

2.25

 

 

 

 

 

 

 

Canceled

 

 

(3,060,506

)

 

 

5.10

 

 

 

 

 

 

 

Outstanding December 31, 2023

 

 

10,398,250

 

 

$

3.34

 

 

 

8.87

 

 

$

28,278

 

Options vested or expected to vest as of December 31, 2023

 

 

10,398,250

 

 

$

3.34

 

 

 

8.87

 

 

$

28,278

 

Stock options exercisable as of December 31, 2023

 

 

1,765,282

 

 

$

4.88

 

 

 

6.97

 

 

$

3,016

 

 

Other information related to the option activity for the years ended December 31, 2023 and 2022:

 

 

Year Ended
December 31,

 

 

 

2023

 

 

2022

 

Weighted-average fair value of options granted

 

$

2.17

 

 

$

2.80

 

Intrinsic value of options exercised (in thousands)

 

 

152

 

 

 

62

 

 

As of December 31, 2023, the unrecognized compensation cost related to outstanding options was $18.8 million, which is expected to be recognized over a weighted-average period of 3.24 years.