Claude Sonnet 5.5 vs Kimi K3.1 Pro
| Spec | Claude Sonnet 5.5 | Kimi K3.1 Pro |
|---|---|---|
| Respan Index | 73.1 (#2) | 71.1 (#4) |
| Blended price per 1M | $2 | $3.6 |
| Context window | 1M | 1.0M |
| Input / output per 1M | $1 / $5 | $1.8 / $9 |
| Max output | 128K | 1.0M |
| Input | text, vision | text, vision, video |
| Released | 2026-09-28 | 2026-10-23 |
Respan Index by category
Each category is scored 0 to 100, and how far ahead the winner is. Leads under a point are close to even.
| Category | Claude Sonnet 5.5 | Kimi K3.1 Pro |
|---|---|---|
| Coding | 79.6 Claude Sonnet 5.5 | 67.8 Kimi K3.1 Pro |
| Agents | 78.4 Claude Sonnet 5.5 | 69.3 Kimi K3.1 Pro |
| Reasoning | 79.0 Claude Sonnet 5.5 | 83.6* Kimi K3.1 Pro |
| Knowledge & language | 48.5 Claude Sonnet 5.5 | 71.2* Kimi K3.1 Pro |
| Human preference | 60.2 Claude Sonnet 5.5 | 58.5 Kimi K3.1 Pro |
* Estimated: no published scores in that category. How the Respan Index works
Benchmarks both report
Claude Sonnet 5.5 leads on 4 of the 4 benchmarks both report. Higher is better. Each score links to where it was published.
| Benchmark | Claude Sonnet 5.5 | Kimi K3.1 Pro |
|---|---|---|
| LMArena Agent (LMArena) | 0.1384 | 0.0596 |
| LMArena WebDev (LMArena) | 1770 | 1695 |
| Terminal-Bench 4.0 (Vals AI) | 64.1% | 63.6% |
| Terminal-Bench 4.0 | 70.6% | 65.7% |
FAQ
Is Claude Sonnet 5.5 better than Kimi K3.1 Pro?
Claude Sonnet 5.5 scores 73.1 on the Respan Index (#2), ahead of Kimi K3.1 Pro at 71.1 (#4). Claude Sonnet 5.5 leads on 4 of the 4 benchmarks both report.
Which is cheaper, Claude Sonnet 5.5 or Kimi K3.1 Pro?
Claude Sonnet 5.5 lists at $1 input and $5 output per 1M tokens; Kimi K3.1 Pro at $1.8 and $9. Claude Sonnet 5.5 is 1.8x cheaper per token at list price.
Which has the larger context window?
Claude Sonnet 5.5 accepts 1M tokens and Kimi K3.1 Pro 1.0M tokens.