GPT-5.1 Pro vs GPT-5.1 Reasoning: which model should you choose?
We compared GPT-5.1 Pro and GPT-5.1 Reasoning on price, context window and 12 benchmarks. GPT-5.1 Reasoning has the stronger average benchmark score; GPT-5.1 Reasoning is cheaper on a blended 3:1 basis.
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
GPT-5.1 Reasoning
GPT-5.1 Reasoning is a frontier model from OpenAI. It offers a 400,000-token context window, costs $20.27 per million input tokens and $82.11 per million output tokens, and averages 88.3 across the index's benchmark suite.
- Input
- $20.27 / 1M
- Output
- $82.11 / 1M
- Context
- 400,000
- Avg score
- 88.3
- Open weights
- No
Specification comparison
| Spec | GPT-5.1 Pro | GPT-5.1 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.77 | $20.27 | A |
| Output price / 1M | $100.32 | $82.11 | B |
| Context window | 200,000 | 400,000 | B |
| Max output | 32,768 | 128,000 | B |
| Average score | 87.8 | 88.3 | B |
| Arena Elo | 1490.0 | 1485.9 | A |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 Pro wins 5, GPT-5.1 Reasoning wins 7, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 Pro | GPT-5.1 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 86.2 | 90.0 | 3.8 | GPT-5.1 Reasoning |
| GPQA Diamond | 83.4 | 85.6 | 2.2 | GPT-5.1 Reasoning |
| SWE-bench Verified | 80.1 | 76.0 | 4.1 | GPT-5.1 Pro |
| HumanEval | 91.1 | 92.9 | 1.8 | GPT-5.1 Reasoning |
| MATH-500 | 95.1 | 95.9 | 0.8 | GPT-5.1 Reasoning |
| AIME 2025 | 90.6 | 85.0 | 5.6 | GPT-5.1 Pro |
| LiveCodeBench | 82.2 | 80.9 | 1.3 | GPT-5.1 Pro |
| IFEval | 94.8 | 94.6 | 0.2 | GPT-5.1 Pro |
| TruthfulQA | 86.9 | 90.0 | 3.1 | GPT-5.1 Reasoning |
| HellaSwag | 93.8 | 94.4 | 0.6 | GPT-5.1 Reasoning |
| MMMU | 81.6 | 86.2 | 4.6 | GPT-5.1 Reasoning |
| Arena Elo | 1490.0 | 1485.9 | 4.1 | GPT-5.1 Pro |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 Pro costs about $39.91 per million tokens and GPT-5.1 Reasoning costs about $35.73. GPT-5.1 Reasoning is roughly 10% 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.
GPT-5.1 Reasoning has the larger context window at 400,000 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, GPT-5.1 Pro wins 5, GPT-5.1 Reasoning wins 7, and 0 are tied. On the index average, GPT-5.1 Reasoning leads GPT-5.1 Pro by 0.5 points (88.3 versus 87.8).
The price picture favours GPT-5.1 Reasoning. The context picture favours GPT-5.1 Reasoning. 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 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose GPT-5.1 Pro if
- You prefer OpenAI's tooling or already use it.
Choose GPT-5.1 Reasoning 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 400,000-token context window.
- You need the larger 128,000-token output limit.
FAQ
Is GPT-5.1 Pro better than GPT-5.1 Reasoning?
On the index average, GPT-5.1 Reasoning leads GPT-5.1 Pro by 0.5 points (88.3 versus 87.8). The better choice depends on price, context and your task. GPT-5.1 Pro wins 5 benchmarks, GPT-5.1 Reasoning wins 7.
Which is cheaper, GPT-5.1 Pro or GPT-5.1 Reasoning?
GPT-5.1 Reasoning is cheaper on a blended 3:1 basis at about $35.73 per million tokens, versus $39.91 for GPT-5.1 Pro.
Which has the larger context window?
GPT-5.1 Reasoning has the larger context window at 400,000 tokens. GPT-5.1 Pro has 200,000 tokens.
Are these models open weights?
GPT-5.1 Pro is proprietary; GPT-5.1 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.