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STOCKHOLDERS' EQUITY (Tables) | 12 Months Ended
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Dec. 31, 2024
Stockholders' Equity Note [Abstract] |
Schedule of aggregate stock option and award activity | Aggregate stock option and award activity for the 2011 Plan, 2018 Plan, Inducement Plan and Directors Market Plan is as follows:
|  |  |  |  | Outstanding Stock Options |
|  |  |  |  |  |  |  |  |  |  | Weighted Average |  |  |  |
|  | Shares |  |  |  |  |  | Weighted Average |  |  | Remaining |  |  | Aggregate |
|  | Available |  |  | Number of |  |  | Exercise Price |  |  | Contractual Life |  |  | Intrinsic |
|  | For Grant |  |  | Shares |  |  | Per Share |  |  | (In years) |  |  | Value |
Balance at December 31, 2023 |  |  | 58,750,670 |  |  |  | 72,984,351 |  |  | $ | 2.16 |  |  |  |  |  |  |
Stock options granted |  |  | (29,603,740 | ) |  |  | 29,603,740 |  |  | $ | 2.86 |  |  |  |  |  |  |
Awards granted |  |  | (8,351 | ) |  |  | — |  |  | $ | — |  |  |  |  |  |  |
Stock options exercised |  |  | — |  |  |  | (17,907,649 | ) |  | $ | 1.77 |  |  |  |  |  |  |
Stock options cancelled/forfeited/expired |  |  | 5,171,390 |  |  |  | (8,713,075 | ) |  | $ | 3.24 |  |  |  |  |  |  |
Balance at December 31, 2024 |  |  | 34,309,969 |  |  |  | 75,967,367 |  | (1) | $ | 2.40 |  |  |  | 7.35 |  |  | $ | 94,204,849 |
Stock options exercisable at December 31, 2024 |  |  |  |  |  | 37,943,520 |  |  | $ | 2.06 |  |  |  | 5.84 |  |  | $ | 57,488,305 |
Stock options fully vested and expected to vest at December 31, 2024 |  |  |  |  |  | 74,159,549 |  |  | $ | 2.39 |  |  |  | 7.30 |  |  | $ | 92,613,420 |
(1) Includes 300,000 performance-based stock options granted that have not achieved the specified performance milestone.
Summary of allocation of stock-based compensation expense related to share-based payment awards | The following table summarizes the stock‑based compensation expense related to service-based stock options and employee stock purchases for the years ended December 31, 2024, 2023 and 2022, which was allocated as follows:
|  | Year Ended December 31, |
(In thousands) |  | 2024 |  |  | 2023 |  |  | 2022 |
Research and development |  | $ | 10,280 |  |  | $ | 7,426 |  |  | $ | 3,720 |
General and administrative |  |  | 21,647 |  |  |  | 11,099 |  |  |  | 4,281 |
Total Stock-based compensation expense |  | $ | 31,927 |  |  | $ | 18,525 |  |  | $ | 8,001 |
Schedule of assumptions used to estimate the fair value of stock options granted | The fair value of stock options granted in 2024, 2023, and 2022 has been estimated at the date of grant using the Black-Scholes option‑pricing model with the following assumptions:
|  | Year Ended December 31,
|  | 2024 |  | 2023 |  | 2022
Dividend yield |  | 0% |  | 0% |  | 0%
Expected volatility range |  | 0.72 to 0.87 |  | 0.82 to 0.83 |  | 0.77 to 0.82
Risk-free interest rate range |  | 3.5% to 4.6% |  | 3.42% to 4.94% |  | 1.69% to 4.57%
Expected term range |  | 6.0 yrs |  | 6.0 yrs |  | 5.5 yrs
Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan | The fair value of employee stock purchases in 2024, 2023, and 2022 has been estimated using the Black-Scholes option‑pricing model with the following assumptions:
|  | Year Ended December 31,
|  | 2024 |  | 2023 |  | 2022
Dividend yield |  | 0% |  | 0% |  | 0%
Expected volatility range |  | 0.72. to 1.19 |  | 0.79 to 0.83 |  | 0.61 to 0.87
Risk-free interest rate range |  | 4.8% to 5.4% |  | 4.73% to 5.4% |  | 0.40% to 2.79%
Expected term range |  | 6 - 12 mos |  | 6 - 12 mos |  | 6 - 12 mos
Schedule of common stock reserved for future issuance | Common stock reserved for future issuance as of December 31, 2024 is as follows:
Outstanding stock options |  |  | 75,967,367 |
Stock options and awards available for grant |  |  | 34,309,969 |
Employee stock purchase plan |  |  | 258,366 |
Warrants outstanding |  |  | 60,835,667 |
Total |  |  | 171,371,369 |

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