Same standard of work. About 5.8× the energy.
Claude Sonnet 5.5 scores higher than Kimi K2.5 on Epoch's Capabilities Index, 166.18 against 148.07, across 58 benchmarks covering coding, agents, long context and writing, while using about 5.8× less energy per answer. In blind head-to-head voting, people rate them 1473 and 1445 respectively.
| Claude Sonnet 5.5 | Kimi K2.5 | |
|---|---|---|
| Energy per answer | 5.64 Wh | 32.9 Wh |
| Carbon released | 2.6 g CO₂ | 15 g CO₂ |
| Same carbon as driving | 10 metres (34 feet) | 61 metres (199 feet) |
| Energy rank | 193 of 278 | 257 of 278 |
| Capability (58 benchmarks) | 166.2 | 148.1 |
| Human vote rating | 1473 | 1445 |
| Votes cast | 10,033 | 74,682 |
| Confidence | Day-one estimate | Day-one estimate |
| Released | 2026-09-28 | 2026-01-27 |
Energy is calculated the same way for every model on this site, from public data and calibrated against laboratory measurement, accurate to roughly a factor of two to three, which is why we only ever state a difference of 5× or more. Capability is Epoch AI's Capabilities Index, one score combining 58 separate benchmarks; the vote rating comes from blind human comparisons. The full method is here.