Stock-based Compensation

6 Months Ended

Jun. 30, 2026

Share-Based Payment Arrangement [Abstract]

9. Stock-based Compensation

2017 Stock Incentive Plan

In December 2017, we adopted the 2017 Stock Incentive Plan (the “2017 Plan”), as amended and restated, pursuant to which we have outstanding stock options. No future awards may be granted under the 2017 Plan.

2021 Stock Incentive Plan

In April 2021, our board of directors adopted and our stockholders approved the 2021 Stock Incentive Plan (the “2021 Plan”), which became effective immediately prior to the effectiveness of our initial public offering (the “IPO”). As a result of the adoption of the 2021 Plan, no further awards will be made under the 2017 Plan.

The 2021 Plan provides for the grant of incentive stock options (“ISOs”), non-qualified stock options, restricted stock awards (“RSAs”), restricted stock units (“RSUs”), stock appreciation rights and other stock-based awards. Our employees, officers, directors, consultants and advisors are eligible to receive awards under the 2021 Plan. The terms of awards, including vesting requirements, are determined by our board of directors, subject to the provisions of the 2021 Plan.

We initially registered 3,352,725 shares of common stock under the 2021 Plan, pursuant to a Registration Statement on Form S-8 filed with the SEC on April 30, 2021, which was comprised of (i) 2,843,116 shares of common stock reserved for issuance under the 2021 Plan, (ii) 31,884 shares of common stock originally reserved for issuance under the 2017 Plan that became available for issuance under the 2021 Plan upon the completion of the IPO, and (iii) 477,725 shares of unvested restricted stock subject to repurchase by us that may become issuable under the 2021 Plan following such repurchase. The 2021 Plan also provides that an additional number of shares will be added annually to the shares authorized for issuance under the 2021 Plan on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2022 and continuing until, and including, the fiscal year ending December 31, 2031. The number of shares added each year will be equal to the lesser of (i) 5% of the number of shares of outstanding common stock on such date and (ii) such amount as determined by our board of directors. As of June 30, 2026, a cumulative total of 9,582,699 additional shares have been added to the total shares authorized for issuance under the 2021 Plan in accordance with these terms.

2021 Employee Stock Purchase Plan

The 2021 Employee Stock Purchase Plan (“2021 ESPP”) permits eligible employees to purchase shares of our common stock at a discount and consists of consecutive six-month offering periods, each containing a single six-month purchase period. On the first day of each offering period, each employee who is enrolled in the 2021 ESPP will automatically receive an option to purchase up to a whole number of shares of our common stock. The purchase price of each of the shares purchased, in a given purchase period, will be equal to 85% of the lesser of the closing price of a share of our common stock on (i) the first day of the offering period, or (ii) the last day of the offering period. During the six months ended June 30, 2026 and 2025, 2,249 and 39,853 shares of our common stock, respectively, were purchased by participants of the 2021 ESPP.

Stock-Based Compensation Expense

Total stock-based compensation expense recognized in our condensed consolidated statements of operations was as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2026		2025		2026		2025
	(in thousands)
Research and development	$	83	$	973	$	586	$	2,028
General and administrative	336		820		762		1,771
Total stock-based compensation	$	419	$	1,793	$	1,348	$	3,799

As part of the severance benefits offered to former employees impacted by the 2026 Restructuring described in Note 2 (the “Former Employees”), the forfeiture conditions of outstanding stock options belonging to the Former Employees were modified such that the Former Employees will retain their rights to exercise their stock options through the original expiration dates of each respective stock option to the extent that such stock options had become vested at the time that the Former Employees’ employment with us was terminated. Absent these modifications, the impacted stock options would have been forfeited by the Former Employees after a period of 90 days following the termination of their employment with us, if not exercised sooner. The expiration date for all stock options impacted by these modifications will occur on the tenth anniversary of the grant date of each respective stock option. For the three and six months ended June 30, 2026, the stock-based compensation expense above includes $0.1 million and $0.7 million, respectively, of expense recognized related to these modifications.

Stock Option Activity

No stock options were granted during the three or six months ended June 30, 2026. The fair value of stock options granted during the three and six months ended June 30, 2025 were calculated on the date of grant using the following weighted-average assumptions:


	Three Months Ended June 30, 2025		Six Months Ended June 30, 2025

Risk-free interest rate	4.0	%	4.4	%
Expected term (in years)	5.8		5.9
Expected annual dividend yield	—	%	—	%
Expected volatility	95.2	%	95.3	%

Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the three and six months ended June 30, 2025 was $0.82 and $1.17 per share, respectively.

The following table summarizes stock option activity during the six months ended June 30, 2026:


	Options Outstanding
	Number of Options	Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2025	9,954,872	$	4.71
Granted	—	$	—
Exercised	—	$	—
Cancelled	(1,748,441)	$	2.23
Outstanding at June 30, 2026	8,206,431	$	5.24	6.35	$	—
Exercisable at June 30, 2026	6,948,699	$	5.77	6.02	$	—

No stock options were exercised during the three and six months ended June 30, 2026 and 2025.

As of June 30, 2026, we had unrecognized stock-based compensation expense related to unvested stock options of $2.0 million, which we expect to recognize over a weighted-average period of approximately 1.7 years.