GPT-6.1 Sol vs Kimi K3 vs Claude Sonnet 5.5
GPT-6.1 Sol comes out ahead, 69 to 65 and 60 on our weighted score.
- Our pick
OpenAIGPT-6.1 Sol
69/100- ECI—
- Price$2.00 / $10.00
- Context1.05M
Moonshot AIKimi K3
60/100- ECI157.6
- Price$3.00 / $15.00
- Context1.05M
AnthropicClaude Sonnet 5.5
65/100- ECI165.2
- Price$2.00 / $10.00
- Context1M
GPT-6.1 Sol is our pick
GPT-6.1 Sol is the better all-round choice, scoring 69/100 against Claude Sonnet 5.5 (65) and Kimi K3 (60). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified), because GPT-6.1 Sol has no Capabilities Index score yet.
- CapabilityGPT-6.1 SolShared benchmarks: GPT-6.1 Sol 90.7% · Claude Sonnet 5.5 82.7% · Kimi K3 78.3%
- Lowest priceGPT-6.1 Sol and Claude Sonnet 5.5GPT-6.1 Sol $4.00 · Claude Sonnet 5.5 $4.00 · Kimi K3 $6.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6.1 Sol and Kimi K3GPT-6.1 Sol 1,050,000 · Kimi K3 1,048,576 · Claude Sonnet 5.5 1,000,000 tokens
- Widest inputsSame inputsGPT-6.1 Sol: Text, Images, PDFs · Kimi K3: Text, Images, Video · Claude Sonnet 5.5: Text, Images, PDFs
- Self-hostingKimi K3Publishes downloadable weights
| Measure | Weight | GPT-6.1 Sol | Kimi K3 | Claude Sonnet 5.5 |
|---|---|---|---|---|
| CapabilityShared benchmarks | 50% | 91 | 78 | 83 |
| Price | 25% | 21 | 13 | 21 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 61 | 61 | 60 |
| Overall | 100% | 69/100 | 60/100 | 65/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-6.1 SolOpenAI | Kimi K3Moonshot AI | Claude Sonnet 5.5Anthropic |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | — | 157.6 | 165.2 (best) |
| ECI rank | — | #13 of 148 | #3 of 148 (best) |
| GPQA DiamondGraduate-level science questions | 95.4% | 93.1% | 95.6% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 93.7% (best) | 72.2% | 88.8% |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% (best) | 97.2% | 100% (best) |
| SimpleQA VerifiedShort factual questions | 73.9% (best) | 50.6% | 46.5% |
| Price per million tokens | |||
| Input | $2.00 (best) | $3.00 | $2.00 (best) |
| Output | $10.00 (best) | $15.00 | $10.00 (best) |
| Cached input | $0.10 (best) | $0.30 | $0.20 |
| Blended (3:1) | $4.00 (best) | $6.00 | $4.00 (best) |
| Long-context rate | Over 272K: $4.00 / $15.00 | Same rate | Same rate |
| Price source | Official OpenAI API | Official Moonshot AI API | Official Anthropic API |
| Limits | |||
| Context window | 1,050,000 tokens (best) | 1,048,576 tokens | 1,000,000 tokens |
| Max output | 128,000 tokens | 131,072 tokens (best) | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | No | Yes |
| Audio | No | No | No |
| Video | No | Yes | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · high · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Open | Proprietary |
| API model ID | gpt-6.1-sol | kimi-k3 | claude-sonnet-5-5 |
| API providers | 21 | 68 (best) | 23 |
| Released | Sep 29, 2026 | Jul 16, 2026 | Sep 28, 2026 |
| Knowledge cutoff | Apr 30, 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-6.1 Sol$40.00
- Kimi K3$60.00
- Claude Sonnet 5.5$40.00
Which should you choose?
Which is better: GPT-6.1 Sol, Kimi K3 or Claude Sonnet 5.5?
GPT-6.1 Sol is the better all-round choice, scoring 69/100 against Claude Sonnet 5.5 (65) and Kimi K3 (60). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified), because GPT-6.1 Sol has no Capabilities Index score yet.
Which is cheaper, GPT-6.1 Sol, Kimi K3 or Claude Sonnet 5.5?
GPT-6.1 Sol is cheaper at $2.00 input / $10.00 output per million tokens (official OpenAI API price). Claude Sonnet 5.5 costs $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 GPT-6.1 Sol versus $4.00 for Claude Sonnet 5.5 (1× as much) and $6.00 for Kimi K3 (1.5× as much).
Which scores higher on benchmarks?
Not every model here has a Capabilities Index score, so we compare the average of shared benchmarks (GPQA Diamond, FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified): GPT-6.1 Sol 90.7%, Claude Sonnet 5.5 82.7% and Kimi K3 78.3%. On individual benchmarks: GPQA Diamond — Claude Sonnet 5.5 95.6%, GPT-6.1 Sol 95.4%, Kimi K3 93.1%; FrontierMath Tiers 1–3 — GPT-6.1 Sol 93.7%, Claude Sonnet 5.5 88.8%, Kimi K3 72.2%; OTIS Mock AIME 2024–2025 — GPT-6.1 Sol 100%, Claude Sonnet 5.5 100%, Kimi K3 97.2%; SimpleQA Verified — GPT-6.1 Sol 73.9%, Kimi K3 50.6%, Claude Sonnet 5.5 46.5%.
Which is better for coding?
There are no published SWE-bench Verified results for GPT-6.1 Sol, Kimi K3 and Claude Sonnet 5.5 yet, so there is no like-for-like coding score. On overall capability, GPT-6.1 Sol 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-6.1 Sol 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-6.1 Sol up to 128,000, Kimi K3 up to 131,072, Claude Sonnet 5.5 up to 128,000 tokens.
Which can read images, PDFs, audio or video?
GPT-6.1 Sol accepts text, images and PDFs; Kimi K3 accepts text, images and video; Claude Sonnet 5.5 accepts text, images and PDFs. 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-6.1 Sol and Claude Sonnet 5.5 is proprietary.
Which is newer?
GPT-6.1 Sol is the newest, released Sep 29, 2026. Claude Sonnet 5.5 came out Sep 28, 2026; Kimi K3 came out Jul 16, 2026. Knowledge cutoff: GPT-6.1 Sol Apr 30, 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 Oct 4, 2026.
