Gemini 2.5 Pro Pro vs Gemini 3 Flash Reasoning: which model should you choose?
We compared Gemini 2.5 Pro Pro and Gemini 3 Flash Reasoning on price, context window and 12 benchmarks. Gemini 3 Flash Reasoning has the stronger average benchmark score; Gemini 3 Flash Reasoning is cheaper on a blended 3:1 basis.
Gemini 2.5 Pro Pro
Gemini 2.5 Pro Pro is a frontier model from Google DeepMind. It offers a 400,000-token context window, costs $17.16 per million input tokens and $90.89 per million output tokens, and averages 83.6 across the index's benchmark suite.
- Input
- $17.16 / 1M
- Output
- $90.89 / 1M
- Context
- 400,000
- Avg score
- 83.6
- Open weights
- No
Gemini 3 Flash Reasoning
Gemini 3 Flash Reasoning is a frontier model from Google DeepMind. It offers a 128,000-token context window, costs $17.05 per million input tokens and $66.77 per million output tokens, and averages 83.7 across the index's benchmark suite.
- Input
- $17.05 / 1M
- Output
- $66.77 / 1M
- Context
- 128,000
- Avg score
- 83.7
- Open weights
- No
Specification comparison
| Spec | Gemini 2.5 Pro Pro | Gemini 3 Flash Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $17.16 | $17.05 | B |
| Output price / 1M | $90.89 | $66.77 | B |
| Context window | 400,000 | 128,000 | A |
| Max output | 8,192 | 32,768 | B |
| Average score | 83.6 | 83.7 | B |
| Arena Elo | 1460.2 | 1446.9 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 2.5 Pro Pro wins 5, Gemini 3 Flash Reasoning wins 7, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Gemini 2.5 Pro Pro | Gemini 3 Flash Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 85.2 | 87.2 | 2.0 | Gemini 3 Flash Reasoning |
| GPQA Diamond | 81.6 | 81.8 | 0.2 | Gemini 3 Flash Reasoning |
| SWE-bench Verified | 72.1 | 72.5 | 0.4 | Gemini 3 Flash Reasoning |
| HumanEval | 88.4 | 86.9 | 1.5 | Gemini 2.5 Pro Pro |
| MATH-500 | 86.8 | 86.2 | 0.6 | Gemini 2.5 Pro Pro |
| AIME 2025 | 83.3 | 79.4 | 3.9 | Gemini 2.5 Pro Pro |
| LiveCodeBench | 76.5 | 77.7 | 1.2 | Gemini 3 Flash Reasoning |
| IFEval | 92.0 | 90.2 | 1.8 | Gemini 2.5 Pro Pro |
| TruthfulQA | 85.5 | 86.6 | 1.1 | Gemini 3 Flash Reasoning |
| HellaSwag | 90.6 | 92.2 | 1.6 | Gemini 3 Flash Reasoning |
| MMMU | 78.1 | 79.8 | 1.7 | Gemini 3 Flash Reasoning |
| Arena Elo | 1460.2 | 1446.9 | 13.3 | Gemini 2.5 Pro Pro |
Price analysis
On a blended 3:1 input-to-output basis, Gemini 2.5 Pro Pro costs about $35.59 per million tokens and Gemini 3 Flash Reasoning costs about $29.48. Gemini 3 Flash Reasoning is roughly 17% cheaper than Gemini 2.5 Pro Pro. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Gemini 2.5 Pro Pro has the larger context window at 400,000 tokens, compared with 128,000 for Gemini 3 Flash Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 2.5 Pro Pro wins 5, Gemini 3 Flash Reasoning wins 7, and 0 are tied. On the index average, Gemini 3 Flash Reasoning leads Gemini 2.5 Pro Pro by 0.1 points (83.7 versus 83.6).
The price picture favours Gemini 3 Flash Reasoning. The context picture favours Gemini 2.5 Pro Pro. 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 Gemini 3 Flash Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Gemini 2.5 Pro Pro if
- You need the larger 400,000-token context window.
Choose Gemini 3 Flash 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 32,768-token output limit.
FAQ
Is Gemini 2.5 Pro Pro better than Gemini 3 Flash Reasoning?
On the index average, Gemini 3 Flash Reasoning leads Gemini 2.5 Pro Pro by 0.1 points (83.7 versus 83.6). The better choice depends on price, context and your task. Gemini 2.5 Pro Pro wins 5 benchmarks, Gemini 3 Flash Reasoning wins 7.
Which is cheaper, Gemini 2.5 Pro Pro or Gemini 3 Flash Reasoning?
Gemini 3 Flash Reasoning is cheaper on a blended 3:1 basis at about $29.48 per million tokens, versus $35.59 for Gemini 2.5 Pro Pro.
Which has the larger context window?
Gemini 2.5 Pro Pro has the larger context window at 400,000 tokens. Gemini 3 Flash Reasoning has 128,000 tokens.
Are these models open weights?
Gemini 2.5 Pro Pro is proprietary; Gemini 3 Flash Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with Gemini 3 Flash Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.