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Stock-based Compensation - Narrative (Details) $ / shares in Units, $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | 62 Months Ended
--- | --- | --- | --- | --- | ---
Apr. 30, 2021 shares | Jun. 30, 2026 USD ($) shares | Jun. 30, 2025 $ / shares shares | Jun. 30, 2026 USD ($) shares | Jun. 30, 2025 $ / shares shares | Dec. 31, 2021 | Jun. 30, 2026 USD ($) shares
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Granted (in shares) |  | 0 |  | 0 |  |  |
Weighted-average grant date fair value of awards (in usd per share) | $ / shares |  |  | $ 0.82 |  | $ 1.17 |  |
Stock option exercises (in shares) |  | 0 | 0 | 0 | 0 |  |
Share-based compensation expense not yet recognized | $ |  | $ 2.0 |  | $ 2.0 |  |  | $ 2.0
2026 Restructuring Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
One-time charge related to modification | $ |  | $ 0.1 |  | $ 0.7 |  |  |
Shares reserved for issuance under the 2021 Stock Incentive Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Stock option expiration period upon termination |  |  |  | 90 days |  |  |
Share-based compensation not yet recognized, recognition period |  |  |  | 1 year 8 months 12 days |  |  |
Shares reserved for issuance under the 2021 Stock Incentive Plan | 2026 Restructuring Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Stock option expiration period |  |  |  | 10 years |  |  |
2021 Stock Incentive Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Maximum number of shares to be added annually, as a percentage of outstanding shares (percent) | 5.00% |  |  |  |  |  |
2021 Stock Incentive Plan | Common stock to be issued upon exercise of the K2HV Loan Agreement conversion feature |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Common stock authorized to be issued (in shares) | 477,725 |  |  |  |  |  |
2021 Stock Employee Stock Purchase Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Offering period |  |  |  |  |  | 6 months |
Purchase period |  |  |  |  |  | 6 months |
ESPP purchase price, percent |  |  |  |  |  | 0.85 |
Common Stock |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Common stock authorized to be issued (in shares) | 3,352,725 |  |  |  |  |  |
Common Stock | 2021 Stock Incentive Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Common stock authorized to be issued (in shares) | 2,843,116 |  |  |  |  |  |
Maximum number of shares to be added annually, as a percentage of outstanding shares (in shares) |  |  |  |  |  |  | 9,582,699
Common Stock | 2017 Stock Incentive Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Common stock authorized to be issued (in shares) | 31,884 |  |  |  |  |  |
Common Stock | 2021 Stock Employee Stock Purchase Plan |  |  |  |  |  |  |
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] |  |  |  |  |  |  |
Shares purchased by employees (in shares) |  |  |  | 2,249 | 39,853 |  |

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