Gemini 3 Pro Reasoning vs GPT-5.1 Reasoning: which model should you choose?
We compared Gemini 3 Pro Reasoning 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.
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 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 | Gemini 3 Pro Reasoning | GPT-5.1 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.69 | $20.27 | A |
| Output price / 1M | $98.36 | $82.11 | B |
| Context window | 200,000 | 400,000 | B |
| Max output | 8,192 | 128,000 | B |
| Average score | 87.5 | 88.3 | B |
| Arena Elo | 1485.0 | 1485.9 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 3 Pro Reasoning 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 | Gemini 3 Pro Reasoning | GPT-5.1 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 90.1 | 90.0 | 0.1 | Gemini 3 Pro Reasoning |
| GPQA Diamond | 83.9 | 85.6 | 1.7 | GPT-5.1 Reasoning |
| SWE-bench Verified | 76.3 | 76.0 | 0.3 | Gemini 3 Pro Reasoning |
| HumanEval | 90.2 | 92.9 | 2.7 | GPT-5.1 Reasoning |
| MATH-500 | 93.3 | 95.9 | 2.6 | GPT-5.1 Reasoning |
| AIME 2025 | 88.8 | 85.0 | 3.8 | Gemini 3 Pro Reasoning |
| LiveCodeBench | 82.0 | 80.9 | 1.1 | Gemini 3 Pro Reasoning |
| IFEval | 93.8 | 94.6 | 0.8 | GPT-5.1 Reasoning |
| TruthfulQA | 90.3 | 90.0 | 0.3 | Gemini 3 Pro Reasoning |
| HellaSwag | 93.5 | 94.4 | 0.9 | GPT-5.1 Reasoning |
| MMMU | 80.8 | 86.2 | 5.4 | GPT-5.1 Reasoning |
| Arena Elo | 1485.0 | 1485.9 | 0.9 | GPT-5.1 Reasoning |
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 Reasoning costs about $35.73. GPT-5.1 Reasoning is roughly 9% cheaper than Gemini 3 Pro Reasoning. 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 Gemini 3 Pro Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 3 Pro Reasoning wins 5, GPT-5.1 Reasoning wins 7, and 0 are tied. On the index average, GPT-5.1 Reasoning leads Gemini 3 Pro Reasoning by 0.8 points (88.3 versus 87.5).
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 Gemini 3 Pro Reasoning if
- You prefer Google DeepMind'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 Gemini 3 Pro Reasoning better than GPT-5.1 Reasoning?
On the index average, GPT-5.1 Reasoning leads Gemini 3 Pro Reasoning by 0.8 points (88.3 versus 87.5). The better choice depends on price, context and your task. Gemini 3 Pro Reasoning wins 5 benchmarks, GPT-5.1 Reasoning wins 7.
Which is cheaper, Gemini 3 Pro Reasoning 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 $39.36 for Gemini 3 Pro Reasoning.
Which has the larger context window?
GPT-5.1 Reasoning has the larger context window at 400,000 tokens. Gemini 3 Pro Reasoning has 200,000 tokens.
Are these models open weights?
Gemini 3 Pro Reasoning 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.