Claude Sonnet 4.5 Pro vs GPT-5.1 Turbo: which model should you choose?
We compared Claude Sonnet 4.5 Pro and GPT-5.1 Turbo on price, context window and 12 benchmarks. Claude Sonnet 4.5 Pro has the stronger average benchmark score; Claude Sonnet 4.5 Pro is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5 Pro
Claude Sonnet 4.5 Pro is a frontier model from Anthropic. It offers a 1,000,000-token context window, costs $18.73 per million input tokens and $82.29 per million output tokens, and averages 86.7 across the index's benchmark suite.
- Input
- $18.73 / 1M
- Output
- $82.29 / 1M
- Context
- 1,000,000
- Avg score
- 86.7
- 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 Pro | GPT-5.1 Turbo | Edge |
|---|---|---|---|
| Input price / 1M | $18.73 | $19.19 | A |
| Output price / 1M | $82.29 | $89.83 | A |
| Context window | 1,000,000 | 2,000,000 | B |
| Max output | 16,384 | 128,000 | B |
| Average score | 86.7 | 86.1 | A |
| Arena Elo | 1469.0 | 1482.0 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Pro wins 7, GPT-5.1 Turbo wins 5, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Pro | GPT-5.1 Turbo | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 86.3 | 85.2 | 1.1 | Claude Sonnet 4.5 Pro |
| GPQA Diamond | 83.1 | 81.3 | 1.8 | Claude Sonnet 4.5 Pro |
| SWE-bench Verified | 73.9 | 74.7 | 0.8 | GPT-5.1 Turbo |
| HumanEval | 92.7 | 91.5 | 1.2 | Claude Sonnet 4.5 Pro |
| MATH-500 | 90.1 | 91.4 | 1.3 | GPT-5.1 Turbo |
| AIME 2025 | 88.4 | 84.7 | 3.7 | Claude Sonnet 4.5 Pro |
| LiveCodeBench | 81.9 | 84.6 | 2.7 | GPT-5.1 Turbo |
| IFEval | 94.1 | 93.4 | 0.7 | Claude Sonnet 4.5 Pro |
| TruthfulQA | 86.1 | 89.2 | 3.1 | GPT-5.1 Turbo |
| HellaSwag | 92.6 | 91.3 | 1.3 | Claude Sonnet 4.5 Pro |
| MMMU | 84.5 | 79.7 | 4.8 | Claude Sonnet 4.5 Pro |
| Arena Elo | 1469.0 | 1482.0 | 13.0 | GPT-5.1 Turbo |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 Pro costs about $34.62 per million tokens and GPT-5.1 Turbo costs about $36.85. Claude Sonnet 4.5 Pro is roughly 6% 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 1,000,000 for Claude Sonnet 4.5 Pro. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 Pro wins 7, GPT-5.1 Turbo wins 5, and 0 are tied. On the index average, Claude Sonnet 4.5 Pro leads GPT-5.1 Turbo by 0.6 points (86.7 versus 86.1).
The price picture favours Claude Sonnet 4.5 Pro. 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 Pro for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Sonnet 4.5 Pro 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 Pro better than GPT-5.1 Turbo?
On the index average, Claude Sonnet 4.5 Pro leads GPT-5.1 Turbo by 0.6 points (86.7 versus 86.1). The better choice depends on price, context and your task. Claude Sonnet 4.5 Pro wins 7 benchmarks, GPT-5.1 Turbo wins 5.
Which is cheaper, Claude Sonnet 4.5 Pro or GPT-5.1 Turbo?
Claude Sonnet 4.5 Pro is cheaper on a blended 3:1 basis at about $34.62 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 Pro has 1,000,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Pro 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 Pro for quality-sensitive work, and check whether its price holds at your expected volume before committing.