Claude Opus 4.5 Reasoning vs GPT-5.1 Max: which model should you choose?
We compared Claude Opus 4.5 Reasoning and GPT-5.1 Max on price, context window and 12 benchmarks. Claude Opus 4.5 Reasoning has the stronger average benchmark score; GPT-5.1 Max is cheaper on a blended 3:1 basis.
Claude Opus 4.5 Reasoning
Claude Opus 4.5 Reasoning is a frontier model from Anthropic. It offers a 2,000,000-token context window, costs $20.91 per million input tokens and $108.13 per million output tokens, and averages 88.2 across the index's benchmark suite.
- Input
- $20.91 / 1M
- Output
- $108.13 / 1M
- Context
- 2,000,000
- Avg score
- 88.2
- Open weights
- No
GPT-5.1 Max
GPT-5.1 Max is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $20.50 per million input tokens and $103.98 per million output tokens, and averages 87.9 across the index's benchmark suite.
- Input
- $20.50 / 1M
- Output
- $103.98 / 1M
- Context
- 2,000,000
- Avg score
- 87.9
- Open weights
- No
Specification comparison
| Spec | Claude Opus 4.5 Reasoning | GPT-5.1 Max | Edge |
|---|---|---|---|
| Input price / 1M | $20.91 | $20.50 | B |
| Output price / 1M | $108.13 | $103.98 | B |
| Context window | 2,000,000 | 2,000,000 | Tie |
| Max output | 16,384 | 8,192 | A |
| Average score | 88.2 | 87.9 | A |
| Arena Elo | 1497.5 | 1478.2 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Opus 4.5 Reasoning wins 7, GPT-5.1 Max wins 5, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Opus 4.5 Reasoning | GPT-5.1 Max | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 90.7 | 91.3 | 0.6 | GPT-5.1 Max |
| GPQA Diamond | 82.6 | 86.4 | 3.8 | GPT-5.1 Max |
| SWE-bench Verified | 79.5 | 75.6 | 3.9 | Claude Opus 4.5 Reasoning |
| HumanEval | 92.1 | 92.2 | 0.1 | GPT-5.1 Max |
| MATH-500 | 91.6 | 91.3 | 0.3 | Claude Opus 4.5 Reasoning |
| AIME 2025 | 88.9 | 88.8 | 0.1 | Claude Opus 4.5 Reasoning |
| LiveCodeBench | 81.8 | 80.2 | 1.6 | Claude Opus 4.5 Reasoning |
| IFEval | 95.9 | 92.2 | 3.7 | Claude Opus 4.5 Reasoning |
| TruthfulQA | 89.0 | 91.1 | 2.1 | GPT-5.1 Max |
| HellaSwag | 93.8 | 93.1 | 0.7 | Claude Opus 4.5 Reasoning |
| MMMU | 84.6 | 85.1 | 0.5 | GPT-5.1 Max |
| Arena Elo | 1497.5 | 1478.2 | 19.3 | Claude Opus 4.5 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, Claude Opus 4.5 Reasoning costs about $42.72 per million tokens and GPT-5.1 Max costs about $41.37. GPT-5.1 Max is roughly 3% cheaper than Claude Opus 4.5 Reasoning. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Both models list a 2,000,000-token context window. That is enough for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Opus 4.5 Reasoning wins 7, GPT-5.1 Max wins 5, and 0 are tied. On the index average, Claude Opus 4.5 Reasoning leads GPT-5.1 Max by 0.3 points (88.2 versus 87.9).
The price picture favours GPT-5.1 Max. The context picture is effectively a tie. 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 Opus 4.5 Reasoning for quality-sensitive work and GPT-5.1 Max for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Claude Opus 4.5 Reasoning if
- You want the higher average benchmark score in this index.
- You need the larger 16,384-token output limit.
Choose GPT-5.1 Max if
- Unit cost matters and you want the cheaper blended price.
FAQ
Is Claude Opus 4.5 Reasoning better than GPT-5.1 Max?
On the index average, Claude Opus 4.5 Reasoning leads GPT-5.1 Max by 0.3 points (88.2 versus 87.9). The better choice depends on price, context and your task. Claude Opus 4.5 Reasoning wins 7 benchmarks, GPT-5.1 Max wins 5.
Which is cheaper, Claude Opus 4.5 Reasoning or GPT-5.1 Max?
GPT-5.1 Max is cheaper on a blended 3:1 basis at about $41.37 per million tokens, versus $42.72 for Claude Opus 4.5 Reasoning.
Which has the larger context window?
Both models list a 2,000,000-token context window.
Are these models open weights?
Claude Opus 4.5 Reasoning is proprietary; GPT-5.1 Max is proprietary.
Which should I choose for production?
If you need a single default, start with Claude Opus 4.5 Reasoning for quality-sensitive work and GPT-5.1 Max for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.