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Equity Incentive Plans (Tables)
12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Fair Value of Stock Option Award Granted
The following assumptions were used to estimate the fair value of stock option awards granted to employees under the Company’s equity incentive plans and the shares purchasable under the ESPP during the periods presented:
Year Ended December 31,
202420232022
Employee Stock Options
Expected term (in years)
4.6 - 6.1
1.0 - 7.0
4.4 - 6.1
Risk-free interest rate
3.59% - 4.50%
3.36% - 4.73%
1.31% - 4.35%
Volatility
100.72% - 104.51%
70.01% - 170.69%
71.10% - 89.87%
Dividend yield
Employee Stock Purchase Plan
Expected term (in years)
0.5 - 2.0
0.5 - 2.0
0.5 - 2.0
Risk-free interest rate
3.88% -5.27%
4.87% - 5.47%
0.60% - 3.51%
Volatility
83.96% - 151.54%
115.19% - 216.45%
64.98% - 121.43%
Dividend yield
Schedule of Stock Option Activity
The following table summarizes stock option activity for the years ended December 31, 2024, 2023 and 2022:
Shares Subject to
Options Outstanding
Weighted-
Average
Remaining
Contractual
Life
(Years)
Aggregate
Intrinsic Value
SharesWeighted-
Average
Exercise
Price
(in thousands)
Outstanding as of December 31, 20219,434,660 $12.24 7.4$15,822 
Options granted9,271,272 $6.75 
Options exercised(270,707)$6.41 
Options forfeited/cancelled(948,060)$15.69 
Outstanding as of December 31, 202217,487,165 $9.24 8.1$47 
Options granted17,159,617 $1.16 
Options exercised— $— 
Options forfeited/cancelled(11,020,667)$11.07 
Outstanding as of December 31, 202323,626,115 $2.52 7.9$369 
Options granted13,006,228 $0.96 
Options exercised— $— 
Options forfeited/cancelled(2,216,006)$2.25 
Outstanding as of December 31, 202434,416,337 $1.95 7.5$598 
Options vested and expected to vest as of December 31, 2024
34,416,337 $1.95 7.5$598 
Options exercisable as of December 31, 2024
14,126,062 $3.20 6.1$100 
Schedule of Restricted Stock Activity
The summary of the Company’s restricted stock activity during the years ended December 31, 2024, 2023 and 2022 is as follows: 
Number of
Restricted
Stock Units
Outstanding
Weighted-
Average
Grant Date
Fair Value
Nonvested at December 31, 20212,561,219 $8.67 
Granted572,901 11.94 
Vested(1,592,588)7.78 
Forfeited / cancelled(191,497)10.68 
Nonvested at December 31, 20221,350,035 $10.83 
Granted— — 
Vested(779,900)10.67 
Forfeited / cancelled(142,437)11.39 
Nonvested at December 31, 2023427,698 $10.92 
Granted— — 
Vested(427,698)10.92 
Forfeited / cancelled— — 
Nonvested at December 31, 2024— $— 
Schedule of Stock-Based Compensation Expense Reported in Condensed Consolidated Statements of Operations
Stock-based compensation expense has been reported in the Company’s consolidated statements of operations and comprehensive loss as follows (in thousands):
Year Ended December 31,
202420232022
Research and development$10,172 $15,871 $24,415 
General and administrative10,447 12,647 18,138 
Total stock-based compensation expense$20,619 $28,518 $42,553