Gemini 3 Pro vs o3 Reasoning: which model should you choose?
We compared Gemini 3 Pro and o3 Reasoning on price, context window and 12 benchmarks. Gemini 3 Pro has the stronger average benchmark score; o3 Reasoning is cheaper on a blended 3:1 basis.
Gemini 3 Pro
Gemini 3 Pro is a frontier model from Google DeepMind. It offers a 2,000,000-token context window, costs $18.24 per million input tokens and $82.93 per million output tokens, and averages 86.1 across the index's benchmark suite.
- Input
- $18.24 / 1M
- Output
- $82.93 / 1M
- Context
- 2,000,000
- Avg score
- 86.1
- Open weights
- No
o3 Reasoning
o3 Reasoning is a frontier model from OpenAI. It offers a 200,000-token context window, costs $18.07 per million input tokens and $70.65 per million output tokens, and averages 85.3 across the index's benchmark suite.
- Input
- $18.07 / 1M
- Output
- $70.65 / 1M
- Context
- 200,000
- Avg score
- 85.3
- Open weights
- No
Specification comparison
| Spec | Gemini 3 Pro | o3 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $18.24 | $18.07 | B |
| Output price / 1M | $82.93 | $70.65 | B |
| Context window | 2,000,000 | 200,000 | A |
| Max output | 8,192 | 16,384 | B |
| Average score | 86.1 | 85.3 | A |
| Arena Elo | 1460.7 | 1456.9 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 3 Pro wins 9, o3 Reasoning wins 3, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Gemini 3 Pro | o3 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 88.2 | 87.7 | 0.5 | Gemini 3 Pro |
| GPQA Diamond | 79.0 | 79.6 | 0.6 | o3 Reasoning |
| SWE-bench Verified | 78.5 | 74.1 | 4.4 | Gemini 3 Pro |
| HumanEval | 91.8 | 91.3 | 0.5 | Gemini 3 Pro |
| MATH-500 | 89.9 | 92.0 | 2.1 | o3 Reasoning |
| AIME 2025 | 84.3 | 80.5 | 3.8 | Gemini 3 Pro |
| LiveCodeBench | 83.3 | 82.7 | 0.6 | Gemini 3 Pro |
| IFEval | 93.7 | 90.6 | 3.1 | Gemini 3 Pro |
| TruthfulQA | 88.8 | 86.5 | 2.3 | Gemini 3 Pro |
| HellaSwag | 91.3 | 90.9 | 0.4 | Gemini 3 Pro |
| MMMU | 78.6 | 82.3 | 3.7 | o3 Reasoning |
| Arena Elo | 1460.7 | 1456.9 | 3.8 | Gemini 3 Pro |
Price analysis
On a blended 3:1 input-to-output basis, Gemini 3 Pro costs about $34.41 per million tokens and o3 Reasoning costs about $31.22. o3 Reasoning is roughly 9% cheaper than Gemini 3 Pro. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Gemini 3 Pro has the larger context window at 2,000,000 tokens, compared with 200,000 for o3 Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 3 Pro wins 9, o3 Reasoning wins 3, and 0 are tied. On the index average, Gemini 3 Pro leads o3 Reasoning by 0.8 points (86.1 versus 85.3).
The price picture favours o3 Reasoning. The context picture favours Gemini 3 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 Pro for quality-sensitive work and o3 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 if
- You want the higher average benchmark score in this index.
- You need the larger 2,000,000-token context window.
Choose o3 Reasoning if
- Unit cost matters and you want the cheaper blended price.
- You need the larger 16,384-token output limit.
FAQ
Is Gemini 3 Pro better than o3 Reasoning?
On the index average, Gemini 3 Pro leads o3 Reasoning by 0.8 points (86.1 versus 85.3). The better choice depends on price, context and your task. Gemini 3 Pro wins 9 benchmarks, o3 Reasoning wins 3.
Which is cheaper, Gemini 3 Pro or o3 Reasoning?
o3 Reasoning is cheaper on a blended 3:1 basis at about $31.22 per million tokens, versus $34.41 for Gemini 3 Pro.
Which has the larger context window?
Gemini 3 Pro has the larger context window at 2,000,000 tokens. o3 Reasoning has 200,000 tokens.
Are these models open weights?
Gemini 3 Pro is proprietary; o3 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with Gemini 3 Pro for quality-sensitive work and o3 Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.