Claude Sonnet 5.5 vs Kimi K3
Claude Sonnet 5.5 comes out ahead, 72 to 65 on our weighted score, and it is the cheaper option too.
- Our pick
AnthropicClaude Sonnet 5.5
72/100- ECI165.2
- Price$2.00 / $10.00
- Context1M
Moonshot AIKimi K3
65/100- ECI157.6
- Price$3.00 / $15.00
- Context1.05M
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Make it a three-way comparison.
Claude Sonnet 5.5 is our pick
Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against Kimi K3 (65). It leads on capability and price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityClaude Sonnet 5.5Capabilities Index (ECI): Claude Sonnet 5.5 165.2 · Kimi K3 157.6
- Lowest priceClaude Sonnet 5.5Claude Sonnet 5.5 $4.00 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
- Longest contextKimi K3Kimi K3 1,048,576 · Claude Sonnet 5.5 1,000,000 tokens
- Widest inputsSame inputsClaude Sonnet 5.5: Text, Images, PDFs · Kimi K3: Text, Images, Video
- Self-hostingKimi K3Publishes downloadable weights
| Measure | Weight | Claude Sonnet 5.5 | Kimi K3 |
|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 97 | 88 |
| Price | 25% | 21 | 13 |
| Inputs & features | 15% | 80 | 80 |
| Context window | 10% | 60 | 61 |
| Overall | 100% | 72/100 | 65/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Sonnet 5.5Anthropic | Kimi K3Moonshot AI |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | 165.2 (best) | 157.6 |
| ECI rank | #3 of 148 (best) | #13 of 148 |
| GPQA DiamondGraduate-level science questions | 95.6% (best) | 93.1% |
| FrontierMath Tiers 1–3Research-level mathematics | 88.8% (best) | 72.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 97.2% |
| SimpleQA VerifiedShort factual questions | 46.5% | 50.6% (best) |
| Price per million tokens | ||
| Input | $2.00 (best) | $3.00 |
| Output | $10.00 (best) | $15.00 |
| Cached input | $0.20 (best) | $0.30 |
| Blended (3:1) | $4.00 (best) | $6.00 |
| Long-context rate | Same rate | Same rate |
| Price source | Official Anthropic API | Official Moonshot AI API |
| Limits | ||
| Context window | 1,000,000 tokens | 1,048,576 tokens (best) |
| Max output | 128,000 tokens | 131,072 tokens (best) |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | Yes |
| PDFs | Yes | No |
| Audio | No | No |
| Video | No | Yes |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · high · max |
| Tool calling | Yes | Yes |
| Structured output | Yes | Yes |
| Availability | ||
| Weights | Proprietary | Open |
| API model ID | claude-sonnet-5-5 | kimi-k3 |
| API providers | 23 | 68 (best) |
| Released | Sep 28, 2026 | Jul 16, 2026 |
| Knowledge cutoff | Jun 2026 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Sonnet 5.5$40.00
- Kimi K3$60.00
Which should you choose?
Which is better: Claude Sonnet 5.5 or Kimi K3?
Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against Kimi K3 (65). It leads on capability and price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Sonnet 5.5 or Kimi K3?
Claude Sonnet 5.5 is cheaper at $2.00 input / $10.00 output per million tokens (official Anthropic API price). Kimi K3 costs $3.00 input / $15.00 output per million tokens (official Moonshot AI API price). At a typical mix of three input tokens to one output token, that is $4.00 per million tokens for Claude Sonnet 5.5 versus $6.00 for Kimi K3 (1.5× as much).
Which scores higher on benchmarks?
Claude Sonnet 5.5 scores higher on the Capabilities Index (ECI): Claude Sonnet 5.5 165.2 (#3 of 148) and Kimi K3 157.6 (#13 of 148). Their confidence ranges do not overlap (161.8–169.4 vs 154.9–160.4), so the gap is a real one. On individual benchmarks: GPQA Diamond — Claude Sonnet 5.5 95.6%, Kimi K3 93.1%; FrontierMath Tiers 1–3 — Claude Sonnet 5.5 88.8%, Kimi K3 72.2%; OTIS Mock AIME 2024–2025 — Claude Sonnet 5.5 100%, Kimi K3 97.2%; SimpleQA Verified — Kimi K3 50.6%, Claude Sonnet 5.5 46.5%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Sonnet 5.5 and Kimi K3 yet, so there is no like-for-like coding score. On overall capability, Claude Sonnet 5.5 leads, which tends to carry over to coding, but test on your own codebase. Both support tool calling for agent workflows.
Which has the bigger context window?
Kimi K3 has the largest context window at 1,048,576 tokens, against 1,000,000 for Claude Sonnet 5.5. Maximum output per response: Claude Sonnet 5.5 up to 128,000, Kimi K3 up to 131,072 tokens.
Which can read images, PDFs, audio or video?
Claude Sonnet 5.5 accepts text, images and PDFs; Kimi K3 accepts text, images and video. They handle the same number of input types.
Are any of these open source?
Kimi K3 publishes its weights and can be self-hosted; Claude Sonnet 5.5 is proprietary.
Which is newer?
Claude Sonnet 5.5 is the newest, released Sep 28, 2026. Kimi K3 came out Jul 16, 2026. Knowledge cutoff: Claude Sonnet 5.5 Jun 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
