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Equity Incentive Plans
 9 Months Ended
Sep. 30, 2025
Share-Based Payment Arrangement [Abstract]  
Equity Incentive Plans Equity Incentive Plans
2017 Equity Incentive Plan
In January 2017, our Board of Directors and stockholders approved and adopted the 2017 Equity Incentive Plan (the “2017 Plan”). Under the 2017 Plan, we may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then our employees, officers, directors or consultants. In addition, the number of shares of stock available for issuance under the 2017 Plan were to be automatically increased each January 1, beginning on January 1, 2018, by 4% of the aggregate number of outstanding shares of our common stock as of the immediately preceding December 31 or such lesser number as determined by our Board of Directors. At our annual stockholder meeting on June 12, 2024, the 2017 Plan was amended, eliminating the automatic annual share increase and the number of shares available for issuance was increased by 2,700,000 shares. At our annual stockholder meeting on June 17, 2025, the 2017 Plan was amended and restated to further increase the number of shares available for issuance by 1,650,000 shares. All future share increases will require stockholder approval. As of September 30, 2025, 2,501,977 shares were available for future issuance.
Employee Stock Purchase Plan
In January 2017, our Board of Directors and stockholders approved and adopted the 2017 Employee Stock Purchase Plan (“ESPP”). In addition, the number shares of stock available for issuance under the ESPP will be automatically increased each January 1, beginning on January 1, 2018, by 1% of the aggregate number of outstanding shares of our common stock as of the immediately preceding December 31 or such lesser number as determined by our Board of Directors. The Board of Directors determined that due to sufficient shares being available in the ESPP, the number of shares available as of January 1, 2025 would not increase. As of September 30, 2025, 241,606 shares have been issued under the ESPP and 1,857,201 shares were available for future issuance under the ESPP. Total cash received from the ESPP was approximately $1.0 million during the nine months ended September 30, 2025.
Stock Options
Stock options granted to employees and non-employees generally vest over a four-year period while stock options granted to directors generally vest over a one-year period. Each stock option award has a maximum term of 10 years from the date of grant, subject to earlier cancellation prior to vesting upon cessation of service to us. A summary of the activity related to stock option awards during the nine months ended September 30, 2025 is as follows:
 
Shares
Subject to
Options
Weighted-Average
Exercise
Price per
Share
Weighted-Average
Remaining
Contractual
Term
(in years)
Aggregate
Intrinsic
Value (in
thousands)
Outstanding at January 1, 2025
6,086,289 $25.20 7.63$534 
Granted1,758,243 $14.87 
Exercised(135,771)$11.27 
Forfeitures and cancellations(173,846)$19.11 
Outstanding at September 30, 20257,534,915 $23.18 7.47$68,499 
Exercisable at September 30, 20254,015,784 $27.06 6.46$26,458 
Total cash received from the exercise of stock options was approximately $1.1 million during the nine months ended September 30, 2025.
Time-Based Restricted Stock Units
Each Restricted Stock Unit (“RSU”) represents one equivalent share of our common stock to be issued after satisfying the applicable continued service-based vesting criteria over a specified period. The fair value of these RSUs is based on the closing price of our common stock on the date of the grant. We measure compensation expense over the expected vesting period on a straight-line basis. The RSUs do not entitle the participants to the rights of holders of common stock, such as voting rights, until the shares are issued.
Number of Restricted Stock UnitsWeighted-Average Grant Date Fair Value
Weighted-Average
Remaining
Contractual
Term
(in years)
Aggregate
Intrinsic
Value (in
thousands)
Outstanding at January 1, 20251,227,677 $21.79 1.46$16,254 
Granted614,828 $14.87 
Released(347,297)$21.96 
Forfeitures and cancellations(64,539)$18.81 
Outstanding at September 30, 20251,430,669 $18.91 1.42$43,807 
RSU expected to vest at September 30, 20251,430,669 $18.91 1.42$43,807 
Performance Stock Units
A Performance Stock Unit (“PSU”) represents one equivalent share of our common stock to be issued after achievement of the performance metrics specified in the grant. The fair value of our PSUs is estimated as of the grant date of July 22, 2024, based upon the expected achievement of the performance metrics specified in the grant and the closing market price of our common stock on the date of grant. The grant date fair value is estimated using a Monte Carlo simulation using the following assumptions:
Nine months ended September 30,
2025
Volatility of common stock59.0 %
Risk-free interest rate4.1 %
Contract term (in years)3.9
The compensation expense for the awards is recognized over the requisite service period regardless of whether the market conditions are achieved and will only be adjusted for pre-vesting forfeitures due to the termination of the recipient’s employment with the company prior to the expiration of the requisite service period. The requisite service period over which the compensation expense will be recognized is July 22, 2024 through July 1, 2028.
The following table presents a summary of activity with respect to our PSUs:
Number of Performance Stock UnitsWeighted-Average Grant Date Fair ValueWeighted-Average Remaining Contractual Term (in years)
Outstanding at January 1, 2025504,500 $24.69 3.52
Granted— $— 
Released— $— 
Forfeitures(6,500)$24.69 
Outstanding at September 30, 2025498,000 $24.69 2.78
Stock-Based Compensation Expense
We recognize stock-based compensation expense for awards issued to employees and non-employees over the requisite service period based on the estimated grant-date fair value of such awards. We record the expense for stock-based compensation awards subject to performance-based milestone vesting over the requisite service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions at each reporting date. The estimated fair values of stock option awards granted were determined on the date of grant using the Black-Scholes option valuation model with the following weighted-average assumptions:
Nine Months Ended
September 30,
20252024
Risk-free interest rate4.5 %4.0 %
Expected volatility81.8 %78.3 %
Expected dividend yield— %— %
Expected term (in years)6.356.28
Weighted-average grant date fair value per share$10.98$15.59
We determine the appropriate risk-free interest rate, expected term for employee stock-based awards, contractual term for non-employee stock-based awards, and volatility assumptions. The weighted-average expected option term for employee and non-employee stock-based awards reflects the historical option term. Expected volatility incorporates the historical volatility of our stock price. The risk-free interest rate is based upon U.S. Treasury securities with remaining terms similar to the expected or contractual term of the stock-based payment awards. The assumed dividend yield is based on our expectation of not paying dividends in the foreseeable future.
Total non-cash stock-based compensation expense for all stock awards that was recognized in the consolidated statements of operations and comprehensive loss is as follows:
Three Months Ended
September 30,		Nine Months Ended
September 30,
(in thousands)2025202420252024
Research and development$4,467 $3,959 $13,330 $10,947 
General and administrative4,690 4,230 14,236 14,917 
Total$9,157 $8,189 $27,566 $25,864 
At September 30, 2025, there was $47.7 million of unrecognized compensation cost related to unvested stock option awards, which is expected to be recognized over a remaining weighted-average vesting period of 2.58 years, $22.4 million of
unrecognized cost related to unvested RSU awards, which is expected to be recognized over a period of 2.51 years, $8.6 million of unrecognized cost related to unvested PSU awards, which is expected to be recognized over a period of 2.78 years, and $0.1 million of unrecognized compensation cost related to the ESPP, which is expected to be recognized over a remaining weighted-average vesting period of 0.13 years.