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Stock-based compensation (Tables) | 9 Months Ended
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Sep. 30, 2025
Share-Based Payment Arrangement [Abstract] |
Schedule of stock-based compensation expense | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended September 30, |  | Nine Months Ended September 30,
​ | ​ | 2025 |  | 2024 | ​ | 2025 | ​ | 2024
Stock options | ​ | $ | 1,402 | ​ | $ | 1,316 | ​ | $ | 3,941 | ​ | $ | 2,903
Restricted stock units | ​ |  | 286 | ​ |  | 230 | ​ |  | 817 | ​ |  | 851
Total stock-based compensation expense | ​ | $ | 1,688 | ​ | $ | 1,546 | ​ | $ | 4,758 | ​ | $ | 3,754
Included in: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
General and administrative expense | ​ | $ | 1,454 | ​ | $ | 1,311 | ​ | $ | 4,068 | ​ | $ | 3,005
Research and development expense | ​ |  | 234 | ​ |  | 235 | ​ |  | 690 | ​ |  | 749
Total stock-based compensation expense | ​ | $ | 1,688 | ​ | $ | 1,546 | ​ | $ | 4,758 | ​ | $ | 3,754
Schedule of option activity transactions | The following table summarizes stock option activity for the nine months ended September 30, 2025 (in thousands, except share and per share data):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted- |  | ​ | ​
​ | ​ | Number of | ​ | ​ | ​ | ​ | Average | ​ | ​ | ​
​ | ​ | Shares | ​ | Weighted- | ​ | Remaining | ​ | ​ | ​
​ | ​ | Underlying | ​ | Average | ​ | Contractual | ​ | Aggregate
​ | ​ | Outstanding | ​ | Exercise | ​ | Term | ​ | Intrinsic
​ | ​ | Options | ​ | Price | ​ | (in Years) | ​ | Value (1)
Outstanding, January 1, 2025 |  | 4,462,517 | ​ | $ | 6.58 |  | 7.4 | ​ | $ | 619
Granted |  | 1,276,597 | ​ | ​ | 4.83 |  | ​ | ​ |  | ​
Exercised | ​ | (44,792) | ​ | ​ | 6.14 | ​ | ​ | ​ | ​ | ​
Forfeited/expired |  | (147) | ​ | ​ | 23.05 |  | ​ | ​ |  | ​
Outstanding, September 30, 2025 (2) |  | 5,694,175 | ​ | $ | 6.19 |  | 7.3 | ​ | $ | 7,048
Vested and expected to vest, September 30, 2025 |  | 5,694,175 | ​ | $ | 6.19 |  | 7.3 | ​ | $ | 7,048
Exercisable at September 30, 2025 |  | 3,422,341 | ​ | $ | 6.74 |  | 6.3 | ​ | $ | 2,668
​
| (1) | Aggregate intrinsic value represents the difference between the fair value of the Company’s Series A common stock on the last day of the fiscal period and the exercise price, multiplied by the number of options outstanding.
| (2) | Includes 477,467 performance-based options with a weighted-average exercise price of $6.44, all of which were fully vested and exercisable.
Schedule of restricted stock unit activity | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted-Average
​ |  | Restricted |  | Grant Date
​ |  | Stock Units |  | Fair Value
Outstanding, January 1, 2025 |  | 844,382 | ​ | $ | 2.96
Granted |  | 254,017 | ​ | ​ | 4.71
Vested/released |  | (281,462) | ​ | ​ | 2.96
Outstanding, September 30, 2025 | ​ | 816,937 | ​ | $ | 3.50
Schedule of fair value assumptions | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Nine Months Ended September 30,
​ | ​ | 2025 | ​ | 2024
Expected volatility |  | 95 - 96 | % | ​ | 91 - 96 | %
Risk-free interest rate |  | 4.1 - 4.3 | % | ​ | 3.9 - 4.5 | %
Dividend yield |  | — |  | ​ | — |
Expected term (in years) |  | 5.3 - 6.0 | ​ | ​ | 5.3 - 6.1 | ​

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (e) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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