Gemini 3 Pro Reasoning vs GPT-5.1 Pro: which model should you choose?
We compared Gemini 3 Pro Reasoning and GPT-5.1 Pro on price, context window and 12 benchmarks. GPT-5.1 Pro has the stronger average benchmark score; Gemini 3 Pro Reasoning is cheaper on a blended 3:1 basis.
Gemini 3 Pro Reasoning
Gemini 3 Pro Reasoning is a frontier model from Google DeepMind. It offers a 200,000-token context window, costs $19.69 per million input tokens and $98.36 per million output tokens, and averages 87.5 across the index's benchmark suite.
- Input
- $19.69 / 1M
- Output
- $98.36 / 1M
- Context
- 200,000
- Avg score
- 87.5
- 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 | Gemini 3 Pro Reasoning | GPT-5.1 Pro | Edge |
|---|---|---|---|
| Input price / 1M | $19.69 | $19.77 | A |
| Output price / 1M | $98.36 | $100.32 | A |
| Context window | 200,000 | 200,000 | Tie |
| Max output | 8,192 | 32,768 | B |
| Average score | 87.5 | 87.8 | B |
| Arena Elo | 1485.0 | 1490.0 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 3 Pro Reasoning wins 3, GPT-5.1 Pro wins 9, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Gemini 3 Pro Reasoning | GPT-5.1 Pro | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 90.1 | 86.2 | 3.9 | Gemini 3 Pro Reasoning |
| GPQA Diamond | 83.9 | 83.4 | 0.5 | Gemini 3 Pro Reasoning |
| SWE-bench Verified | 76.3 | 80.1 | 3.8 | GPT-5.1 Pro |
| HumanEval | 90.2 | 91.1 | 0.9 | GPT-5.1 Pro |
| MATH-500 | 93.3 | 95.1 | 1.8 | GPT-5.1 Pro |
| AIME 2025 | 88.8 | 90.6 | 1.8 | GPT-5.1 Pro |
| LiveCodeBench | 82.0 | 82.2 | 0.2 | GPT-5.1 Pro |
| IFEval | 93.8 | 94.8 | 1.0 | GPT-5.1 Pro |
| TruthfulQA | 90.3 | 86.9 | 3.4 | Gemini 3 Pro Reasoning |
| HellaSwag | 93.5 | 93.8 | 0.3 | GPT-5.1 Pro |
| MMMU | 80.8 | 81.6 | 0.8 | GPT-5.1 Pro |
| Arena Elo | 1485.0 | 1490.0 | 5.0 | GPT-5.1 Pro |
Price analysis
On a blended 3:1 input-to-output basis, Gemini 3 Pro Reasoning costs about $39.36 per million tokens and GPT-5.1 Pro costs about $39.91. Gemini 3 Pro Reasoning is roughly 1% 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.
Both models list a 200,000-token context window. That is enough for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 3 Pro Reasoning wins 3, GPT-5.1 Pro wins 9, and 0 are tied. On the index average, GPT-5.1 Pro leads Gemini 3 Pro Reasoning by 0.3 points (87.8 versus 87.5).
The price picture favours Gemini 3 Pro Reasoning. 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 GPT-5.1 Pro for quality-sensitive work and Gemini 3 Pro Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Gemini 3 Pro Reasoning if
- Unit cost matters and you want the cheaper blended price.
Choose GPT-5.1 Pro if
- You want the higher average benchmark score in this index.
- You need the larger 32,768-token output limit.
FAQ
Is Gemini 3 Pro Reasoning better than GPT-5.1 Pro?
On the index average, GPT-5.1 Pro leads Gemini 3 Pro Reasoning by 0.3 points (87.8 versus 87.5). The better choice depends on price, context and your task. Gemini 3 Pro Reasoning wins 3 benchmarks, GPT-5.1 Pro wins 9.
Which is cheaper, Gemini 3 Pro Reasoning or GPT-5.1 Pro?
Gemini 3 Pro Reasoning is cheaper on a blended 3:1 basis at about $39.36 per million tokens, versus $39.91 for GPT-5.1 Pro.
Which has the larger context window?
Both models list a 200,000-token context window.
Are these models open weights?
Gemini 3 Pro Reasoning 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 Gemini 3 Pro Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.