Claude Opus 4.5 Max vs GPT-5.1 Pro: which model should you choose?
We compared Claude Opus 4.5 Max and GPT-5.1 Pro on price, context window and 12 benchmarks. Claude Opus 4.5 Max and GPT-5.1 Pro are effectively tied on the index average; GPT-5.1 Pro is cheaper on a blended 3:1 basis.
Claude Opus 4.5 Max
Claude Opus 4.5 Max is a frontier model from Anthropic. It offers a 1,000,000-token context window, costs $20.90 per million input tokens and $106.51 per million output tokens, and averages 87.8 across the index's benchmark suite.
- Input
- $20.90 / 1M
- Output
- $106.51 / 1M
- Context
- 1,000,000
- Avg score
- 87.8
- 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 Opus 4.5 Max | GPT-5.1 Pro | Edge |
|---|---|---|---|
| Input price / 1M | $20.90 | $19.77 | B |
| Output price / 1M | $106.51 | $100.32 | B |
| Context window | 1,000,000 | 200,000 | A |
| Max output | 16,384 | 32,768 | B |
| Average score | 87.8 | 87.8 | Tie |
| Arena Elo | 1501.9 | 1490.0 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Opus 4.5 Max wins 5, GPT-5.1 Pro wins 6, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Opus 4.5 Max | GPT-5.1 Pro | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 89.5 | 86.2 | 3.3 | Claude Opus 4.5 Max |
| GPQA Diamond | 84.6 | 83.4 | 1.2 | Claude Opus 4.5 Max |
| SWE-bench Verified | 79.5 | 80.1 | 0.6 | GPT-5.1 Pro |
| HumanEval | 91.7 | 91.1 | 0.6 | Claude Opus 4.5 Max |
| MATH-500 | 94.2 | 95.1 | 0.9 | GPT-5.1 Pro |
| AIME 2025 | 89.3 | 90.6 | 1.3 | GPT-5.1 Pro |
| LiveCodeBench | 80.6 | 82.2 | 1.6 | GPT-5.1 Pro |
| IFEval | 94.5 | 94.8 | 0.3 | GPT-5.1 Pro |
| TruthfulQA | 86.9 | 86.9 | 0.0 | Tie |
| HellaSwag | 93.0 | 93.8 | 0.8 | GPT-5.1 Pro |
| MMMU | 82.3 | 81.6 | 0.7 | Claude Opus 4.5 Max |
| Arena Elo | 1501.9 | 1490.0 | 11.9 | Claude Opus 4.5 Max |
Price analysis
On a blended 3:1 input-to-output basis, Claude Opus 4.5 Max costs about $42.30 per million tokens and GPT-5.1 Pro costs about $39.91. GPT-5.1 Pro is roughly 6% cheaper than Claude Opus 4.5 Max. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Claude Opus 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 Opus 4.5 Max wins 5, GPT-5.1 Pro wins 6, and 1 are tied. The two models are effectively tied on the index average at 87.8.
The price picture favours GPT-5.1 Pro. The context picture favours Claude Opus 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 if cost is the constraint and Claude Opus 4.5 Max if context is the constraint. Test both on a sample of your own traffic before committing.
Choose Claude Opus 4.5 Max if
- You need the larger 1,000,000-token context window.
Choose GPT-5.1 Pro if
- Unit cost matters and you want the cheaper blended price.
- You need the larger 32,768-token output limit.
FAQ
Is Claude Opus 4.5 Max better than GPT-5.1 Pro?
The two models are effectively tied on the index average at 87.8. The better choice depends on price, context and your task. Claude Opus 4.5 Max wins 5 benchmarks, GPT-5.1 Pro wins 6.
Which is cheaper, Claude Opus 4.5 Max or GPT-5.1 Pro?
GPT-5.1 Pro is cheaper on a blended 3:1 basis at about $39.91 per million tokens, versus $42.30 for Claude Opus 4.5 Max.
Which has the larger context window?
Claude Opus 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 Opus 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 if cost is the constraint and Claude Opus 4.5 Max if context is the constraint. Test both on a sample of your own traffic before committing.