| Summary of stock option activity |
| | | | | | | | | | | | | | | | | Weighted‑ | | Weighted | | | | | | | Weighted‑ | | Average | | Average | | | | | | | Average | | Grant | | Remaining | | Aggregate | | | Number of | | Exercise | | Date | | Contractual | | Intrinsic | | | Options | | Price | | Fair Value | | Term | | Value | | | | | US$ per | | US$ per | | | | | | | | | option | | option | | Years | | US$ | Outstanding at December 31, 2022 | | 6,286,912 | | 4.80 | | 5.16 | | 8.44 | | 94,990 | Granted | | 3,442,500 | | 1.14 | | 0.72 | | — | | — | Exercised | | (10,000) | | 0.55 | | 5.72 | | — | | — | Forfeited | | (952,530) | | 4.59 | | 3.45 | | — | | — | Outstanding at December 31, 2023 | | 8,766,882 | | 3.39 | | 3.60 | | 8.24 | | 2,011,843 | Granted | | 3,925,945 | | 1.68 | | 1.04 | | — | | — | Exercised | | (185,620) | | 1.02 | | 2.49 | | — | | — | Forfeited | | (483,022) | | 6.13 | | 4.28 | | — | | — | Cancelled | | (2,176,945) | | 3.68 | | 3.96 | | — | | — | Outstanding at December 31, 2024 | | 9,847,240 | | 2.55 | | 2.49 | | 8.36 | | 1,736,202 | Granted | | 3,624,440 | | 1.40 | | 0.87 | | — | | — | Exercised | | (86,469) | | 0.94 | | 0.98 | | — | | — | Forfeited | | (968,857) | | 2.95 | | 4.03 | | — | | — | Outstanding at December 31, 2025 | | 12,416,354 | | 2.20 | | 1.91 | | 8.03 | | 1,660,307 | Vested and expected to vest at December 31, 2025 | | 12,416,354 | | 2.20 | | 1.91 | | 8.03 | | 1,660,307 | Exercisable at December 31, 2024 | | 3,440,384 | | 4.27 | | 5.15 | | 6.49 | | 616,539 | Exercisable at December 31, 2025 | | 5,319,029 | | 3.21 | | 3.24 | | 6.89 | | 759,799 |
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| Summary of Company's RSU activity under the 2021 Plan |
| | | | | | | | | | | | | Weighted | | | | | Weighted‑ | | Average | | | | | Average | | Remaining | | | Number of | | Grant Date | | Contractual | | | RSU shares | | Fair Value | | Term | | | | | US$ per | | | | | | | RSU | | Years | Unvested at December 31, 2023 | | — | | — | | — | Granted | | 988,750 | | 2.10 | | — | Vested | | — | | — | | — | Forfeited | | (16,250) | | 2.10 | | — | Unvested at December 31, 2024 | | 972,500 | | 2.10 | | 3.56 | Granted | | — | | — | | — | Vested | | (234,688) | | 2.10 | | — | Forfeited | | (58,438) | | 2.10 | | — | Unvested at December 31, 2025 | | 679,375 | | 2.10 | | 2.56 |
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| Summary of total share based compensation expenses recognized |
| | | | | | | | | For the years ended December 31, | | | 2023 | | 2024 | | 2025 | | | US$ | | US$ | | US$ | Research and development expenses | | 4,860,548 | | 3,313,833 | | 2,502,472 | Administrative expenses | | 2,411,152 | | 1,595,740 | | 1,239,076 | Total share‑based compensation expenses | | 7,271,700 | | 4,909,573 | | 3,741,548 |
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