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Stock-based Compensation
 12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Stock-based Compensation Stock-based Compensation
2021 Equity Incentive Plan
In June 2021, the Company adopted the 2021 Equity Incentive Plan (“2021 Plan”), which on the date of the underwriting agreement related to the Company’s IPO became effective with an initial reserve of 26,662,087 shares, plus any shares subject to outstanding awards granted under the 2018 Equity Incentive Plan (“2018 Plan”) that, on or after the effectiveness of the 2021 Plan, terminate or expire before exercise or settlement, are not issued because the award is settled in cash, are forfeited because of the failure to vest or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. In addition, the number of shares reserved for issuance under the 2021 Plan automatically increases on January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, in an amount equal to (1) 5% of the total number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding year, or (2) a lesser number of shares determined by the Company’s board of directors no later than December 31 of the immediately preceding year. On January 1, 2024, the Company reserved an additional 12,697,885 shares of common stock for issuance under the 2021 Plan representing 5% of the total common shares outstanding as of December 31, 2023. Under the 2021 Plan, the Company may grant incentive stock options, non-statutory stock options, RSAs, RSUs, stock appreciation rights, performance awards and other stock‑based awards. Terms of stock awards, including vesting requirements, are determined by the Company’s board of directors or by a committee authorized by the Company’s board of directors, subject to provisions of the 2021 Plan. The term of any stock option granted under the 2021 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but may be granted with different vesting terms. In conjunction with adopting the 2021 Plan, the Company discontinued the 2018 Plan with respect to new equity awards.
As of December 31, 2024, 41,180,525 shares were available for future issuance pursuant to the 2021 Plan.
2021 Employee Stock Purchase Plan
In June 2021, the Company adopted the 2021 Employee Stock Purchase Plan (“2021 ESPP”), which became effective immediately prior to the execution of the underwriting agreement related to the Company’s IPO with an initial reserve of 2,470,000 shares. The 2021 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their earnings, subject to plan limitations. Unless otherwise determined by the Company’s board of directors, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first date of an offering or on the purchase date. The number of shares of the Company’s common stock reserved for issuance under the 2021 ESPP automatically increases on January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, by the lesser of (1) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding year, and (2) 4,940,000 shares; provided, however, that the Company’s board of directors may act to provide a lesser increase in number of shares. On January 1, 2024, the Company reserved an additional 2,539,577 shares of common stock for issuance under the 2021 ESPP representing 1% of the total common shares outstanding as of December 31, 2023.
The Company may specify offerings with durations not more than 27 months and may specify shorter purchase periods within each offering. Under the 2021 ESPP, 954,761, 986,391 and 475,363 shares have been issued for the years ended December 31, 2024, 2023 and 2022, respectively.
As of December 31, 2024, 5,046,445 shares were available for future issuance pursuant to the 2021 ESPP.
2018 Equity Incentive Plan
In 2018, the Company established the 2018 Plan that provided for the grant of incentive stock options, non‑statutory stock options, RSAs, RSUs, stock appreciation rights and other stock-based awards. Terms of stock awards, including vesting requirements, were determined by the board of directors or by a committee authorized by the Company’s board of directors, subject to provisions of the 2018 Plan. The term of any stock option granted under the 2018 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but could have been granted with different vesting terms. Pursuant to the terms of the 2021 Plan, any shares subject to outstanding options originally granted under the 2018 Plan that terminate, expire or lapse for any reason without the delivery of shares to the holder thereof become available for issuance pursuant to awards granted under the 2021 Plan. While no shares are available for future issuance under the 2018 Plan, it continues to govern outstanding equity awards granted thereunder.
Stock-based Compensation Expense
Stock-based compensation expense by classification included within the Consolidated Statements of Operations and Comprehensive Loss was as follows (in thousands):
Year Ended December 31,
202420232022
Research and development
$14,577 $18,207 $16,721 
General and administrative
18,567 28,877 65,203 
Total stock-based compensation expense
$33,144 $47,084 $81,924 
Stock Options and RSA Modifications
In November 2023, the Board of Directors of the Company approved, effective November 16, 2023, a one-time repricing of certain stock option awards that had been granted to date under the 2021 Plan and 2018 Plan. The repricing impacted stock options with exercise prices greater than $2.37 held by employees who remained employed as-of November 16, 2023 and were not impacted by the reduction in workforce. The original exercise prices of the repriced stock options ranged from $2.61 to $17.95 per share for 200 total grantees with 23,416,860 shares repriced. Each stock option was repriced to have a per share exercise price of $1.87, which was the closing price of the Company’s common stock on November 16, 2023. To receive the new exercise price, option holders were required to remain employed with the Company through November 15, 2024. Additionally, the vesting schedule for the unvested shares underlying repriced stock options held by executives at the level of senior vice president and above was extended for an additional year. There were no changes to the vesting schedules for employees below the level of senior vice president. No changes were made to the expiration dates of or number of shares underlying the repriced stock options. Incremental stock-based compensation expense resulting from the repricing was $8.9 million in the aggregate. Expense for vested awards will be recognized through November 15, 2024 and expense for unvested awards will be recognized over the remaining service life of the option.
In December 2022, the Company’s former chief executive officer (“CEO”) resigned. Under the terms of the separation agreement, the former CEO will be available to provide consulting services to the Company through June 15, 2024, with vested options continuing to be exercisable and unvested options continuing to vest through that date. The Company concluded that the obligation to provide consulting services was nonsubstantive, and therefore resulted in a modification of their options due to the reduction of their service level. As the remaining service period was determined to be nonsubstantive, the entire incremental expense of $3.7 million associated with the modification was recognized in the fourth quarter of 2022.
At December 31, 2024, total stock-based compensation cost related to unvested awards not yet recognized was $44.7 million, which is expected to be recognized over a remaining weighted-average period of 2.3 years.
Performance-Based Restricted Stock Units
During the year ended December 31, 2024, the Company granted PSU awards to certain key employees. PSUs awarded to employees have a three-year performance period and vest based upon the Company’s performance against a two and three-year relative total shareholder return (“rTSR”) metric, as well as upon the achievement of certain clinical development milestones. Certain of the clinical development milestones were determined to be probable of achievement as of December 31, 2024, representing 1.5 million shares. For the portion of PSUs subject to certain clinical development milestones (other than the bonus clinical development milestone), 50% vest upon the achievement of the applicable milestone, and the remaining 50% vest upon the earlier of (a) one year of service from the date of such achievement and (b) the end of the three-year performance period. The vesting of all PSU awards granted is also subject to the respective employee’s continued employment. The Company valued the portion of PSUs subject to the rTSR metric using a Monte Carlo simulation. The number of PSUs granted subject to the rTSR metrics represents the target number of units that are eligible to be earned based on the achievement of the metrics established at the beginning of the performance period, which ends on December 31st of the three-year performance period. For the portion of PSUs subject to the rTSR metrics, employees may ultimately earn between zero and 200% of the target number of PSUs granted based on the degree of achievement of the applicable rTSR metric. Accordingly, additional PSUs may be issued or currently outstanding PSUs may be cancelled upon final determination of the number of units earned. Stock-based compensation expense recognized for the PSU awards was approximately $1.9 million for the year ended December 31, 2024 and zero for both the years ended December 31, 2023 and 2022.
A summary of the Company’s PSU activity was as follows:
Performance-Based Restricted Stock Units Outstanding
Weighted-Average
Value at Grant
Date Per Share
Unvested PSUs as of December 31, 2023
— $— 
PSUs granted(1)
2,703,400 $1.88 
PSUs vested
— $— 
PSUs forfeited or canceled
— $— 
Unvested PSUs as of December 31, 2024
2,703,400 $1.88 
(1)     PSU grants reflect the target number of shares eligible to be earned at the time of grant.
As of December 31, 2024, none of the PSU metrics have been met, resulting in no shares vesting.
Restricted Stock Awards
The Company had no unvested RSAs as of both December 31, 2024 and 2023. The fair value of RSAs vested during the years ended December 31, 2024, 2023 and 2022 was zero, zero and $15.2 million, respectively.
Restricted Stock Units
A summary of the Company’s RSU activity was as follows:
Number of SharesWeighted-Average
Value at Grant Date
Per Share
Unvested RSUs as of December 31, 2023
2,072,855$2.96 
RSUs granted5,762,499 $1.54 
RSUs vested(1,259,344)$2.55 
RSUs forfeited or canceled(952,191)$2.19 
Unvested RSUs as of December 31, 2024
5,623,819 $1.72 
The fair value of RSUs vested during the years ended December 31, 2024, 2023 and 2022 was $2.0 million, $1.4 million and $1.5 million, respectively.
Stock Options
A summary of the Company’s stock option activity was as follows:
Number of
Stock
Options
Weighted-
Average
Exercise
Price
Per Share
Weighted-
Average
Remaining
Contractual
Life
(in years)		Aggregate
Intrinsic
Value (in thousands)
Options outstanding as of December 31, 2023
55,596,831 $4.75 6.89$7,368 
Granted
3,665,500 $1.90 
Exercised
(1,245,836)$0.12 
Canceled or forfeited
(13,229,412)$6.18 
Options outstanding as of December 31, 2024
44,787,083 $2.49 6.62$1,479 
Options exercisable as of December 31, 2024
30,273,806 $2.74 5.88$1,479 
The fair value of stock options granted to employees, directors and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following weighted-average assumptions:
Year Ended December 31,
202420232022
Risk-free interest rate4.17 %4.13 %2.93 %
Expected volatility75.9 %88.0 %87.3 %
Expected term (in years)5.896.066.03
Expected dividend yield0 %0 %0 %
The weighted-average grant date fair value of options granted for the years ended December 31, 2024, 2023 and 2022 was $1.30 per share, $1.69 per share and $3.60 per share, respectively. The intrinsic value of options exercised during the years ended December 31, 2024, 2023 and 2022 was $2.9 million, $6.5 million and $13.9 million, respectively.