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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Stock-Based Compensation |
Schedule of fair value assumptions | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, | ​ | September 30,
​ | ​ | 2021 | ​ | 2020
Risk-free interest rate |  | ​ | 0.63% |  | ​ | *
Expected term (in years) | ​ | ​ | 5.98 | ​ | ​ | *
Expected volatility | ​ | ​ | 77.07% | ​ | ​ | *
Expected dividend yield |  |  | — | ​ | ​ | *
Schedule of stock option activity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | Weighted | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | ​ | ​
​ | ​ | Number of | ​ | Exercise | ​ | Contractual | ​ | Aggregate
​ | ​ | Shares | ​ | Price | ​ | Term | ​ | Intrinsic Value
​ | ​ | ​ | ​ | ​ | ​ | (in years) | ​ | (in thousands)
Outstanding as of December 31, 2020 |  | 4,776,908 |  | $ | 10.83 |  | 9.67 |  | $ | 177,962
Granted | ​ | 1,031,733 | ​ | ​ | 35.88 | ​ | 9.31 | ​ | ​ | —
Exercised(1) | ​ | (156,385) | ​ | ​ | 3.38 | ​ | — | ​ | ​ | —
Forfeited | ​ | (87,668) | ​ | ​ | 22.39 | ​ | — | ​ | ​ | —
Outstanding as of September 30, 2021(2) | ​ | 5,564,588 | ​ | $ | 15.50 | ​ | 9.03 | ​ | $ | 71,759
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Options vested and exercisable as of September 30, 2021 | ​ | 1,053,721 | ​ | $ | 7.38 | ​ | 8.57 | ​ | $ | 21,315
Options expected to vest as of September 30, 2021 | ​ | 4,510,867 | ​ | $ | 17.39 | ​ | 9.14 | ​ | $ | 54,999
​
(1) | Exercised amount includes vesting of early exercised options.
(2) | Balance as of September 30, 2021 includes 53,588 unvested early exercised stock options.
Summary of restricted stock activity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | Number of Shares | ​ | Grant Date Fair Value
Unvested restricted stock as of December 31, 2020 |  | ​ | 735,294 |  | $ | 2.40
Granted | ​ | ​ | — | ​ | ​ | —
Vested | ​ | ​ | (192,790) | ​ | ​ | 2.40
Forfeited | ​ | ​ | — | ​ | ​ | —
Unvested restricted stock as of September 30, 2021 |  | ​ | 542,504 | ​ | $ | 2.40
Schedule of stock-based compensation expense | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended September 30, | ​ | Nine Months Ended September 30,
​ | ​ | 2021 | ​ | 2020 | ​ | 2021 | ​ | 2020
Research and development |  | $ | 2,405 |  | $ | 392 |  | $ | 6,427 |  | $ | 495
General and administrative |  |  | 1,752 | ​ | ​ | 190 |  |  | 4,859 | ​ | ​ | 241
Total |  | $ | 4,157 | ​ | $ | 582 |  | $ | 11,286 | ​ | $ | 736

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