Claude Sonnet 4.5 Reasoning vs GPT-5.1 Turbo: which model should you choose?
We compared Claude Sonnet 4.5 Reasoning and GPT-5.1 Turbo on price, context window and 12 benchmarks. Claude Sonnet 4.5 Reasoning has the stronger average benchmark score; Claude Sonnet 4.5 Reasoning is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5 Reasoning
Claude Sonnet 4.5 Reasoning is a frontier model from Anthropic. It offers a 400,000-token context window, costs $19.48 per million input tokens and $68.20 per million output tokens, and averages 87.7 across the index's benchmark suite.
- Input
- $19.48 / 1M
- Output
- $68.20 / 1M
- Context
- 400,000
- Avg score
- 87.7
- Open weights
- No
GPT-5.1 Turbo
GPT-5.1 Turbo is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.19 per million input tokens and $89.83 per million output tokens, and averages 86.1 across the index's benchmark suite.
- Input
- $19.19 / 1M
- Output
- $89.83 / 1M
- Context
- 2,000,000
- Avg score
- 86.1
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 Reasoning | GPT-5.1 Turbo | Edge |
|---|---|---|---|
| Input price / 1M | $19.48 | $19.19 | B |
| Output price / 1M | $68.20 | $89.83 | A |
| Context window | 400,000 | 2,000,000 | B |
| Max output | 8,192 | 128,000 | B |
| Average score | 87.7 | 86.1 | A |
| Arena Elo | 1486.5 | 1482.0 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Reasoning wins 8, GPT-5.1 Turbo wins 4, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Reasoning | GPT-5.1 Turbo | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.6 | 85.2 | 2.4 | Claude Sonnet 4.5 Reasoning |
| GPQA Diamond | 85.2 | 81.3 | 3.9 | Claude Sonnet 4.5 Reasoning |
| SWE-bench Verified | 79.6 | 74.7 | 4.9 | Claude Sonnet 4.5 Reasoning |
| HumanEval | 90.3 | 91.5 | 1.2 | GPT-5.1 Turbo |
| MATH-500 | 89.7 | 91.4 | 1.7 | GPT-5.1 Turbo |
| AIME 2025 | 87.3 | 84.7 | 2.6 | Claude Sonnet 4.5 Reasoning |
| LiveCodeBench | 85.1 | 84.6 | 0.5 | Claude Sonnet 4.5 Reasoning |
| IFEval | 91.9 | 93.4 | 1.5 | GPT-5.1 Turbo |
| TruthfulQA | 87.6 | 89.2 | 1.6 | GPT-5.1 Turbo |
| HellaSwag | 95.2 | 91.3 | 3.9 | Claude Sonnet 4.5 Reasoning |
| MMMU | 85.2 | 79.7 | 5.5 | Claude Sonnet 4.5 Reasoning |
| Arena Elo | 1486.5 | 1482.0 | 4.5 | Claude Sonnet 4.5 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 Reasoning costs about $31.66 per million tokens and GPT-5.1 Turbo costs about $36.85. Claude Sonnet 4.5 Reasoning is roughly 14% cheaper than GPT-5.1 Turbo. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
GPT-5.1 Turbo has the larger context window at 2,000,000 tokens, compared with 400,000 for Claude Sonnet 4.5 Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 Reasoning wins 8, GPT-5.1 Turbo wins 4, and 0 are tied. On the index average, Claude Sonnet 4.5 Reasoning leads GPT-5.1 Turbo by 1.6 points (87.7 versus 86.1).
The price picture favours Claude Sonnet 4.5 Reasoning. The context picture favours GPT-5.1 Turbo. Those two dimensions often matter more than a few benchmark points once a model is good enough for the task.
If you need a single default, start with Claude Sonnet 4.5 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Sonnet 4.5 Reasoning if
- You want the higher average benchmark score in this index.
- Unit cost matters and you want the cheaper blended price.
Choose GPT-5.1 Turbo if
- You need the larger 2,000,000-token context window.
- You need the larger 128,000-token output limit.
FAQ
Is Claude Sonnet 4.5 Reasoning better than GPT-5.1 Turbo?
On the index average, Claude Sonnet 4.5 Reasoning leads GPT-5.1 Turbo by 1.6 points (87.7 versus 86.1). The better choice depends on price, context and your task. Claude Sonnet 4.5 Reasoning wins 8 benchmarks, GPT-5.1 Turbo wins 4.
Which is cheaper, Claude Sonnet 4.5 Reasoning or GPT-5.1 Turbo?
Claude Sonnet 4.5 Reasoning is cheaper on a blended 3:1 basis at about $31.66 per million tokens, versus $36.85 for GPT-5.1 Turbo.
Which has the larger context window?
GPT-5.1 Turbo has the larger context window at 2,000,000 tokens. Claude Sonnet 4.5 Reasoning has 400,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Reasoning is proprietary; GPT-5.1 Turbo is proprietary.
Which should I choose for production?
If you need a single default, start with Claude Sonnet 4.5 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.