GPT-5.6 Terra vs Claude Sonnet 5.5 vs Kimi K3
Claude Sonnet 5.5 comes out ahead, 72 to 67 and 65 on our weighted score, and it is the cheaper option too.
OpenAIGPT-5.6 Terra
67/100- ECI160.1
- Price$2.00 / $12.00
- Context1.05M
- Our pick
AnthropicClaude Sonnet 5.5
72/100- ECI166.7
- Price$2.00 / $10.00
- Context1M
Moonshot AIKimi K3
65/100- ECI158.3
- Price$3.00 / $15.00
- Context1.05M
Claude Sonnet 5.5 is our pick
Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against GPT-5.6 Terra (67) and 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 5.5 166.7 · GPT-5.6 Terra 160.1 · Kimi K3 158.3
- Lowest priceClaude Sonnet 5.5Claude Sonnet 5.5 $4.00 · GPT-5.6 Terra $4.50 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
- Longest contextGPT-5.6 Terra and Kimi K3GPT-5.6 Terra 1,050,000 · Kimi K3 1,048,576 · Claude Sonnet 5.5 1,000,000 tokens
- Widest inputsSame inputsGPT-5.6 Terra: Text, Images, PDFs · Claude Sonnet 5.5: Text, Images, PDFs · Kimi K3: Text, Images, Video
- Self-hostingKimi K3Publishes downloadable weights
| Measure | Weight | GPT-5.6 Terra | Claude Sonnet 5.5 | Kimi K3 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 89 | 97 | 87 |
| Price | 25% | 18 | 20 | 12 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 61 | 60 | 61 |
| Overall | 100% | 67/100 | 72/100 | 65/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-5.6 TerraOpenAI | Claude Sonnet 5.5Anthropic | Kimi K3Moonshot AI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 160.1 | 166.7 (best) | 158.3 |
| ECI rank | #15 of 165 | #5 of 165 (best) | #20 of 165 |
| GPQA DiamondGraduate-level science questions | 93.3% | 95.6% (best) | 93.1% |
| FrontierMath Tiers 1–3Research-level mathematics | 86.0% | 88.8% (best) | 72.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 99.7% | 100% (best) | 97.2% |
| SimpleQA VerifiedShort factual questions | 43.2% | 46.5% | 50.6% (best) |
| Price per million tokens | |||
| Input | $2.00 (best) | $2.00 (best) | $3.00 |
| Output | $12.00 | $10.00 (best) | $15.00 |
| Cached input | $0.20 | $0.10 (best) | $0.30 |
| Blended (3:1) | $4.50 | $4.00 (best) | $6.00 |
| Long-context rate | Over 272K: $4.00 / $18.00 | Same rate | Same rate |
| Price source | Official OpenAI API | Official Anthropic API | Official Moonshot AI API |
| Limits | |||
| Context window | 1,050,000 tokens (best) | 1,000,000 tokens | 1,048,576 tokens |
| Max output | 128,000 tokens | 128,000 tokens | 131,072 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | No |
| Audio | No | No | No |
| Video | No | No | Yes |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max | Yeslow · high · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Open |
| API model ID | gpt-5.6-terra | claude-sonnet-5-5 | kimi-k3 |
| API providers | 45 | 34 | 76 (best) |
| Released | Jul 9, 2026 | Sep 28, 2026 | Jul 16, 2026 |
| Knowledge cutoff | Feb 16, 2026 | 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.
- GPT-5.6 Terra$44.00
- Claude Sonnet 5.5$40.00
- Kimi K3$60.00
Which should you choose?
Which is better: GPT-5.6 Terra, Claude Sonnet 5.5 or Kimi K3?
Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against GPT-5.6 Terra (67) and 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, GPT-5.6 Terra, 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). GPT-5.6 Terra costs $2.00 input / $12.00 output per million tokens (official OpenAI 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 $4.50 for GPT-5.6 Terra (1.1× as much) and $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 5.5 166.7 (#5 of 165), GPT-5.6 Terra 160.1 (#15 of 165) and Kimi K3 158.3 (#20 of 165). Their confidence ranges do not overlap (163.6–171.3 vs 157.8–163.4), so the gap is a real one. On individual benchmarks: GPQA Diamond — Claude Sonnet 5.5 95.6%, GPT-5.6 Terra 93.3%, Kimi K3 93.1%; FrontierMath Tiers 1–3 — Claude Sonnet 5.5 88.8%, GPT-5.6 Terra 86.0%, Kimi K3 72.2%; OTIS Mock AIME 2024–2025 — Claude Sonnet 5.5 100%, GPT-5.6 Terra 99.7%, Kimi K3 97.2%; SimpleQA Verified — Kimi K3 50.6%, Claude Sonnet 5.5 46.5%, GPT-5.6 Terra 43.2%.
Which is better for coding?
There are no published SWE-bench Verified results for GPT-5.6 Terra, 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. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-5.6 Terra and Kimi K3 have the largest context windows (1,050,000 and 1,048,576 tokens), against 1,000,000 for Claude Sonnet 5.5. Maximum output per response: GPT-5.6 Terra up to 128,000, Claude Sonnet 5.5 up to 128,000, Kimi K3 up to 131,072 tokens.
Which can read images, PDFs, audio or video?
GPT-5.6 Terra accepts text, images and PDFs; 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; GPT-5.6 Terra and 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; GPT-5.6 Terra came out Jul 9, 2026. Knowledge cutoff: GPT-5.6 Terra Feb 16, 2026, 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 Nov 2, 2026.
