Claude Sonnet 4.5 Turbo vs GPT-5.1: which model should you choose?
We compared Claude Sonnet 4.5 Turbo and GPT-5.1 on price, context window and 12 benchmarks. GPT-5.1 has the stronger average benchmark score; GPT-5.1 is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5 Turbo
Claude Sonnet 4.5 Turbo is a frontier model from Anthropic. It offers a 1,000,000-token context window, costs $18.37 per million input tokens and $81.65 per million output tokens, and averages 85.9 across the index's benchmark suite.
- Input
- $18.37 / 1M
- Output
- $81.65 / 1M
- Context
- 1,000,000
- Avg score
- 85.9
- Open weights
- No
GPT-5.1
GPT-5.1 is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.01 per million input tokens and $69.84 per million output tokens, and averages 86.0 across the index's benchmark suite.
- Input
- $19.01 / 1M
- Output
- $69.84 / 1M
- Context
- 2,000,000
- Avg score
- 86.0
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 Turbo | GPT-5.1 | Edge |
|---|---|---|---|
| Input price / 1M | $18.37 | $19.01 | A |
| Output price / 1M | $81.65 | $69.84 | B |
| Context window | 1,000,000 | 2,000,000 | B |
| Max output | 65,536 | 128,000 | B |
| Average score | 85.9 | 86.0 | B |
| Arena Elo | 1461.7 | 1462.5 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Turbo wins 5, GPT-5.1 wins 6, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Turbo | GPT-5.1 | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.2 | 86.1 | 1.1 | Claude Sonnet 4.5 Turbo |
| GPQA Diamond | 83.7 | 82.3 | 1.4 | Claude Sonnet 4.5 Turbo |
| SWE-bench Verified | 75.2 | 76.1 | 0.9 | GPT-5.1 |
| HumanEval | 90.4 | 90.6 | 0.2 | GPT-5.1 |
| MATH-500 | 88.0 | 90.5 | 2.5 | GPT-5.1 |
| AIME 2025 | 87.8 | 85.6 | 2.2 | Claude Sonnet 4.5 Turbo |
| LiveCodeBench | 78.9 | 78.9 | 0.0 | Tie |
| IFEval | 91.4 | 90.9 | 0.5 | Claude Sonnet 4.5 Turbo |
| TruthfulQA | 87.7 | 89.2 | 1.5 | GPT-5.1 |
| HellaSwag | 93.9 | 92.2 | 1.7 | Claude Sonnet 4.5 Turbo |
| MMMU | 81.1 | 83.3 | 2.2 | GPT-5.1 |
| Arena Elo | 1461.7 | 1462.5 | 0.8 | GPT-5.1 |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 Turbo costs about $34.19 per million tokens and GPT-5.1 costs about $31.72. GPT-5.1 is roughly 7% cheaper than Claude Sonnet 4.5 Turbo. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
GPT-5.1 has the larger context window at 2,000,000 tokens, compared with 1,000,000 for Claude Sonnet 4.5 Turbo. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 Turbo wins 5, GPT-5.1 wins 6, and 1 are tied. On the index average, GPT-5.1 leads Claude Sonnet 4.5 Turbo by 0.1 points (86.0 versus 85.9).
The price picture favours GPT-5.1. The context picture favours GPT-5.1. 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 GPT-5.1 for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Sonnet 4.5 Turbo if
- You prefer Anthropic's tooling or already use it.
Choose GPT-5.1 if
- You want the higher average benchmark score in this index.
- Unit cost matters and you want the cheaper blended price.
- 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 Turbo better than GPT-5.1?
On the index average, GPT-5.1 leads Claude Sonnet 4.5 Turbo by 0.1 points (86.0 versus 85.9). The better choice depends on price, context and your task. Claude Sonnet 4.5 Turbo wins 5 benchmarks, GPT-5.1 wins 6.
Which is cheaper, Claude Sonnet 4.5 Turbo or GPT-5.1?
GPT-5.1 is cheaper on a blended 3:1 basis at about $31.72 per million tokens, versus $34.19 for Claude Sonnet 4.5 Turbo.
Which has the larger context window?
GPT-5.1 has the larger context window at 2,000,000 tokens. Claude Sonnet 4.5 Turbo has 1,000,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Turbo is proprietary; GPT-5.1 is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 for quality-sensitive work, and check whether its price holds at your expected volume before committing.