Claude Sonnet 5.5 vs Claude Fable 5.1 vs GPT-6.1 Sol
GPT-6.1 Sol comes out ahead, 68 to 63 and 61 on our weighted score.
AnthropicClaude Sonnet 5.5
63/100- ECI165.2
- Price$2.00 / $10.00
- Context1M
- Anthropic
Claude Fable 5.1
61/100- ECI164.8
- Price$10.00 / $50.00
- Context1M
- Our pick
OpenAIGPT-6.1 Sol
68/100- ECI—
- Price$2.00 / $10.00
- Context1.05M
GPT-6.1 Sol is our pick
GPT-6.1 Sol is the better all-round choice, scoring 68/100 against Claude Sonnet 5.5 (63) and Claude Fable 5.1 (61). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (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 89.2% · Claude Fable 5.1 87.0% · Claude Sonnet 5.5 78.4%
- Lowest priceClaude Sonnet 5.5 and GPT-6.1 SolClaude Sonnet 5.5 $4.00 · GPT-6.1 Sol $4.00 · Claude Fable 5.1 $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-6.1 SolGPT-6.1 Sol 1,050,000 · Claude Sonnet 5.5 1,000,000 · Claude Fable 5.1 1,000,000 tokens
- Widest inputsSame inputsClaude Sonnet 5.5: Text, Images, PDFs · Claude Fable 5.1: Text, Images, PDFs · GPT-6.1 Sol: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Sonnet 5.5 | Claude Fable 5.1 | GPT-6.1 Sol |
|---|---|---|---|---|
| CapabilityShared benchmarks | 50% | 78 | 87 | 89 |
| Price | 25% | 21 | 0 | 21 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 60 | 60 | 61 |
| Overall | 100% | 63/100 | 61/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Sonnet 5.5Anthropic | Claude Fable 5.1Anthropic | GPT-6.1 SolOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 165.2 (best) | 164.8 | — |
| ECI rank | #3 of 148 (best) | #4 of 148 | — |
| GPQA DiamondGraduate-level science questions | 95.6% (best) | — | 95.4% |
| FrontierMath Tiers 1–3Research-level mathematics | 88.8% | 90.2% | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% | 100% | 100% |
| SimpleQA VerifiedShort factual questions | 46.5% | 70.8% | 73.9% (best) |
| Price per million tokens | |||
| Input | $2.00 (best) | $10.00 | $2.00 (best) |
| Output | $10.00 (best) | $50.00 | $10.00 (best) |
| Cached input | $0.20 | $0.25 | $0.10 (best) |
| Blended (3:1) | $4.00 (best) | $20.00 | $4.00 (best) |
| Long-context rate | Same rate | Same rate | Over 272K: $4.00 / $15.00 |
| Price source | Official Anthropic API | Official Anthropic API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,000,000 tokens | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 128,000 tokens | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | No | No | No |
| Video | No | No | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-sonnet-5-5 | claude-fable-5-1 | gpt-6.1-sol |
| API providers | 23 | 29 (best) | 21 |
| Released | Sep 28, 2026 | Sep 1, 2026 | Sep 29, 2026 |
| Knowledge cutoff | Jun 2026 | Jun 2026 | Apr 30, 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
- Claude Fable 5.1$200.00
- GPT-6.1 Sol$40.00
Which should you choose?
Which is better: Claude Sonnet 5.5, Claude Fable 5.1 or GPT-6.1 Sol?
GPT-6.1 Sol is the better all-round choice, scoring 68/100 against Claude Sonnet 5.5 (63) and Claude Fable 5.1 (61). It leads on capability. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%. Capability uses the average of shared benchmarks (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, Claude Sonnet 5.5, Claude Fable 5.1 or GPT-6.1 Sol?
Claude Sonnet 5.5 is cheaper at $2.00 input / $10.00 output per million tokens (official Anthropic API price). GPT-6.1 Sol costs $2.00 input / $10.00 output per million tokens (official OpenAI API price); Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic 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 $4.00 for GPT-6.1 Sol (1× as much) and $20.00 for Claude Fable 5.1 (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 (FrontierMath Tiers 1–3, OTIS Mock AIME 2024–2025 and SimpleQA Verified): GPT-6.1 Sol 89.2%, Claude Fable 5.1 87.0% and Claude Sonnet 5.5 78.4%. On individual benchmarks: FrontierMath Tiers 1–3 — GPT-6.1 Sol 93.7%, Claude Fable 5.1 90.2%, Claude Sonnet 5.5 88.8%; OTIS Mock AIME 2024–2025 — Claude Sonnet 5.5 100%, Claude Fable 5.1 100%, GPT-6.1 Sol 100%; SimpleQA Verified — GPT-6.1 Sol 73.9%, Claude Fable 5.1 70.8%, Claude Sonnet 5.5 46.5%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Sonnet 5.5, Claude Fable 5.1 and GPT-6.1 Sol 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 has the largest context window at 1,050,000 tokens, against 1,000,000 for Claude Sonnet 5.5 and 1,000,000 for Claude Fable 5.1. Maximum output per response: Claude Sonnet 5.5 up to 128,000, Claude Fable 5.1 up to 128,000, GPT-6.1 Sol up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Sonnet 5.5 accepts text, images and PDFs; Claude Fable 5.1 accepts text, images and PDFs; GPT-6.1 Sol accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
No. Claude Sonnet 5.5, Claude Fable 5.1 and GPT-6.1 Sol are proprietary and only available through APIs and apps.
Which is newer?
GPT-6.1 Sol is the newest, released Sep 29, 2026. Claude Sonnet 5.5 came out Sep 28, 2026; Claude Fable 5.1 came out Sep 1, 2026. Knowledge cutoff: Claude Sonnet 5.5 Jun 2026, Claude Fable 5.1 Jun 2026, GPT-6.1 Sol Apr 30, 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.
