| Summary of stock option activity |
| | | | | | | | | | | | | | | | | Weighted‑ | | | | | | | | | | | Average | | Weighted | | | | | | | Weighted‑ | | Grant | | Average | | | | | | | Average | | Date | | Remaining | | Aggregate | | | Number of | | Exercise | | Fair | | Contractual | | Intrinsic | | | Options | | Price | | Value | | Term | | Value | | | | | US$ per | | US$ per | | | | | | | | | option | | option | | Years | | US$ | Outstanding at December 31, 2024 | | 9,847,240 | | 2.55 | | 2.49 | | 8.36 | | 1,736,202 | Granted | | 3,424,440 | | 1.41 | | 0.88 | | — | | — | Exercised | | (3,250) | | 1.08 | | 0.66 | | — | | — | Forfeited | | (442,646) | | 3.11 | | 2.12 | | — | | — | Outstanding at June 30, 2025 | | 12,825,784 | | 2.23 | | 2.07 | | 8.40 | | 2,046,458 | Outstanding at December 31, 2025 | | 12,416,354 | | 2.20 | | 1.91 | | 8.03 | | 1,660,307 | Granted | | 3,136,333 | | 2.10 | | 1.36 | | — | | — | Exercised | | (326,933) | | 1.27 | | 1.68 | | — | | — | Forfeited | | (105,000) | | 1.96 | | 1.25 | | — | | — | Outstanding at June 30, 2026 | | 15,120,754 | | 2.20 | | 1.80 | | 7.99 | | 25,196,630 | Vested and expected to vest at June 30, 2026 | | 15,120,754 | | 2.20 | | 1.80 | | 7.99 | | 25,196,630 | Exercisable at June 30, 2025 | | 4,863,411 | | 3.49 | | 3.96 | | 6.86 | | 759,771 | Exercisable at June 30, 2026 | | 7,301,789 | | 2.76 | | 2.57 | | 7.02 | | 12,010,060 |
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| Summary of total share based compensation expenses recognized |
| | | | | | | For the Six Months Ended June 30, | | | 2025 | | 2026 | | | US$ | | US$ | Research and development expenses | | 1,393,980 | | 1,373,432 | Administrative expenses | | 636,355 | | 758,326 | Total share‑based compensation expenses | | 2,030,335 | | 2,131,758 |
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