Claude Sonnet 4.5 Max vs GPT-5.1 Pro: which model should you choose?
We compared Claude Sonnet 4.5 Max and GPT-5.1 Pro on price, context window and 12 benchmarks. GPT-5.1 Pro has the stronger average benchmark score; Claude Sonnet 4.5 Max is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5 Max
Claude Sonnet 4.5 Max is a frontier model from Anthropic. It offers a 1,000,000-token context window, costs $19.90 per million input tokens and $95.47 per million output tokens, and averages 87.2 across the index's benchmark suite.
- Input
- $19.90 / 1M
- Output
- $95.47 / 1M
- Context
- 1,000,000
- Avg score
- 87.2
- Open weights
- No
GPT-5.1 Pro
GPT-5.1 Pro is a frontier model from OpenAI. It offers a 200,000-token context window, costs $19.77 per million input tokens and $100.32 per million output tokens, and averages 87.8 across the index's benchmark suite.
- Input
- $19.77 / 1M
- Output
- $100.32 / 1M
- Context
- 200,000
- Avg score
- 87.8
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 Max | GPT-5.1 Pro | Edge |
|---|---|---|---|
| Input price / 1M | $19.90 | $19.77 | B |
| Output price / 1M | $95.47 | $100.32 | A |
| Context window | 1,000,000 | 200,000 | A |
| Max output | 65,536 | 32,768 | A |
| Average score | 87.2 | 87.8 | B |
| Arena Elo | 1474.9 | 1490.0 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Max wins 6, GPT-5.1 Pro wins 6, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Max | GPT-5.1 Pro | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 86.1 | 86.2 | 0.1 | GPT-5.1 Pro |
| GPQA Diamond | 84.4 | 83.4 | 1.0 | Claude Sonnet 4.5 Max |
| SWE-bench Verified | 80.2 | 80.1 | 0.1 | Claude Sonnet 4.5 Max |
| HumanEval | 92.4 | 91.1 | 1.3 | Claude Sonnet 4.5 Max |
| MATH-500 | 92.8 | 95.1 | 2.3 | GPT-5.1 Pro |
| AIME 2025 | 85.4 | 90.6 | 5.2 | GPT-5.1 Pro |
| LiveCodeBench | 82.8 | 82.2 | 0.6 | Claude Sonnet 4.5 Max |
| IFEval | 92.9 | 94.8 | 1.9 | GPT-5.1 Pro |
| TruthfulQA | 87.3 | 86.9 | 0.4 | Claude Sonnet 4.5 Max |
| HellaSwag | 93.1 | 93.8 | 0.7 | GPT-5.1 Pro |
| MMMU | 82.0 | 81.6 | 0.4 | Claude Sonnet 4.5 Max |
| Arena Elo | 1474.9 | 1490.0 | 15.1 | GPT-5.1 Pro |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 Max costs about $38.79 per million tokens and GPT-5.1 Pro costs about $39.91. Claude Sonnet 4.5 Max is roughly 3% cheaper than GPT-5.1 Pro. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Claude Sonnet 4.5 Max has the larger context window at 1,000,000 tokens, compared with 200,000 for GPT-5.1 Pro. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 Max wins 6, GPT-5.1 Pro wins 6, and 0 are tied. On the index average, GPT-5.1 Pro leads Claude Sonnet 4.5 Max by 0.6 points (87.8 versus 87.2).
The price picture favours Claude Sonnet 4.5 Max. The context picture favours Claude Sonnet 4.5 Max. 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 Pro for quality-sensitive work and Claude Sonnet 4.5 Max for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Claude Sonnet 4.5 Max if
- Unit cost matters and you want the cheaper blended price.
- You need the larger 1,000,000-token context window.
- You need the larger 65,536-token output limit.
Choose GPT-5.1 Pro if
- You want the higher average benchmark score in this index.
FAQ
Is Claude Sonnet 4.5 Max better than GPT-5.1 Pro?
On the index average, GPT-5.1 Pro leads Claude Sonnet 4.5 Max by 0.6 points (87.8 versus 87.2). The better choice depends on price, context and your task. Claude Sonnet 4.5 Max wins 6 benchmarks, GPT-5.1 Pro wins 6.
Which is cheaper, Claude Sonnet 4.5 Max or GPT-5.1 Pro?
Claude Sonnet 4.5 Max is cheaper on a blended 3:1 basis at about $38.79 per million tokens, versus $39.91 for GPT-5.1 Pro.
Which has the larger context window?
Claude Sonnet 4.5 Max has the larger context window at 1,000,000 tokens. GPT-5.1 Pro has 200,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Max is proprietary; GPT-5.1 Pro is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 Pro for quality-sensitive work and Claude Sonnet 4.5 Max for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.