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Equity Incentive Plans (Tables) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Share-Based Payment Arrangement [Abstract] |  |
Summary of Assumptions under Employee Stock Purchase Plan |  | Effective January 1, 2022, the number of shares of common stock available under the 2021 ESPP increased by 564,000 shares pursuant to the evergreen provision of the 2021 ESPP.
|  | Year Ended December 31, |
|  | 2022 |  |  | 2021 |
Expected volatility |  |  | 73.00% - 75.00 | % |  |  | 72.00% - 74.00 | %
Expected dividend yield |  |  | 0 | % |  |  | 0 | %
Expected term (in years) |  |  | 0.5 |  |  |  | 0.44 - 0.5 |
Risk-free interest rate |  |  | 0.10% - 4.65 | % |  |  | 0.10% - 1.00 | %
Summary of Assumptions under Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for Stock Option Awards |  | The Company used the Black-Scholes option pricing model to estimate stock-based compensation expense for stock option awards granted during the periods presented, with the following assumptions.
|  | Year Ended December 31, |
|  | 2022 |  |  | 2021 |
Expected volatility |  |  | 74.00% - 75.00 | % |  |  | 72.00% - 77.74 | %
Expected dividend yield |  |  | 0 | % |  |  | 0 | %
Expected term (in years) |  |  | 5.97 - 6.01 |  |  |  | 5.48 - 6.04 |
Risk-free interest rate |  |  | 1.91% - 4.23 | % |  |  | 0.56% - 1.34 | %
Summary of Option Activity | A summary of option activity under the 2020 Plan and the 2021 Plan during the nine months ended September 30, 2023 is as follows:
|  | Number of Options |  |  | Weighted- Average Exercise Price Per Share |  |  | Weighted- Average Remaining Contractual Term (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding as of December 31, 2022 |  |  | 7,755,303 |  |  | $ | 8.47 |  |  |  | 8.67 |  |  | $ | 794 |
Options granted—2021 Plan |  |  | 3,223,400 |  |  | $ | 2.22 |  |  |  |  |  |  |  |  |
Options exercised |  |  | (65,414 | ) |  | $ | 0.52 |  |  |  |  |  |  |  |  |
Options cancelled |  |  | (4,532,774 | ) |  | $ | 6.50 |  |  |  |  |  |  |  |  |
Outstanding as of September 30, 2023 |  |  | 6,380,515 |  |  | $ | 6.79 |  |  |  | 5.6 |  |  | $ | 695 |
Exercisable |  |  | 4,231,849 |  |  | $ | 6.86 |  |  |  | 4.4 |  |  | $ | 472 |
Vested and expected to vest as of September 30, 2023 |  |  | 6,380,515 |  |  | $ | 6.79 |  |  |  | 5.6 |  |  | $ | 695 |
| A summary of option activity under the 2020 Plan and the 2021 Plan during the year ended December 31, 2022 is as follows:
|  | Number of Options |  |  | Weighted- Average Exercise Price Per Share |  |  | Weighted- Average Remaining Contractual Term (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding as of December 31, 2021 |  |  | 5,056,743 |  |  | $ | 8.77 |  |  |  | 9.2 |  |  | $ | 18,503 |
Options granted—2021 Plan |  |  | 3,292,702 |  |  | $ | 7.91 |  |  |  |  |  |  |  |  |
Options exercised |  |  | (67,196 | ) |  | $ | 0.30 |  |  |  |  |  |  |  |  |
Options cancelled |  |  | (526,946 | ) |  | $ | 8.99 |  |  |  |  |  |  |  |  |
Outstanding as of December 31, 2022 |  |  | 7,755,303 |  |  | $ | 8.47 |  |  |  | 8.7 |  |  | $ | 794 |
Exercisable |  |  | 2,330,389 |  |  | $ | 8.74 |  |  |  | 8.3 |  |  | $ | 388 |
Vested and expected to vest as of December 31, 2022 |  |  | 7,755,303 |  |  | $ | 8.47 |  |  |  | 8.7 |  |  | $ | 794 |
Components of Stock-based Compensation Expense | The following table presents the components of stock-based compensation expense for the Company’s stock-based awards for the periods presented (in thousands):
|  | Three Months Ended September 30, |  |  | Nine Months Ended September 30, |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Restricted stock awards and founders’ common stock awards |  | $ | 1 |  |  | $ | 2 |  |  | $ | 5 |  |  | $ | 6 |
ESPP |  |  | 1 |  |  |  | 58 |  |  |  | 96 |  |  |  | 316 |
Stock options |  |  | 2,159 |  |  |  | 3,150 |  |  |  | 8,168 |  |  |  | 9,590 |
Total stock-based compensation expense |  | $ | 2,161 |  |  | $ | 3,210 |  |  | $ | 8,269 |  |  | $ | 9,912 |
| The following table presents the components of stock-based compensation expense for the Company’s stock-based awards for the periods presented (in thousands):
|  | Year Ended December 31, |
|  | 2022 |  |  | 2021 |
Restricted stock awards and founders’ common stock awards |  | $ | 11 |  |  | $ | 9 |
ESPP |  |  | 391 |  |  |  | 215 |
Stock options |  |  | 13,132 |  |  |  | 7,647 |
Total stock-based compensation expense |  | $ | 13,534 |  |  | $ | 7,871 |
Classification of Stock-based Compensation Expense | The following table presents the classification of stock-based compensation expense for the Company’s stock-based awards for the periods presented (in thousands):
|  | Three Months Ended September 30, |  |  | Nine Months Ended September 30, |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Research and development expenses |  | $ | 37 |  |  | $ | 1,249 |  |  | $ | 1,904 |  |  | $ | 3,881 |
General and administrative expenses |  |  | 2,124 |  |  |  | 1,961 |  |  |  | 6,365 |  |  |  | 6,031 |
Total stock-based compensation expense |  | $ | 2,161 |  |  | $ | 3,210 |  |  | $ | 8,269 |  |  | $ | 9,912 |
| The following table presents the classification of stock-based compensation expense for the Company’s stock-based awards for the periods presented (in thousands):
|  | Year Ended December 31, |
|  | 2022 |  |  | 2021 |
Research and development expenses |  | $ | 5,317 |  |  | $ | 2,685 |
General and administrative expenses |  |  | 8,217 |  |  |  | 5,186 |
Total stock-based compensation expense |  | $ | 13,534 |  |  | $ | 7,871 |

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