Gemini 2.5 Pro Reasoning vs o3: which model should you choose?
We compared Gemini 2.5 Pro Reasoning and o3 on price, context window and 12 benchmarks. o3 has the stronger average benchmark score; Gemini 2.5 Pro Reasoning is cheaper on a blended 3:1 basis.
Gemini 2.5 Pro Reasoning
Gemini 2.5 Pro Reasoning is a frontier model from Google DeepMind. It offers a 128,000-token context window, costs $16.81 per million input tokens and $67.95 per million output tokens, and averages 83.8 across the index's benchmark suite.
- Input
- $16.81 / 1M
- Output
- $67.95 / 1M
- Context
- 128,000
- Avg score
- 83.8
- Open weights
- No
o3
o3 is a frontier model from OpenAI. It offers a 400,000-token context window, costs $16.80 per million input tokens and $81.80 per million output tokens, and averages 84.5 across the index's benchmark suite.
- Input
- $16.80 / 1M
- Output
- $81.80 / 1M
- Context
- 400,000
- Avg score
- 84.5
- Open weights
- No
Specification comparison
| Spec | Gemini 2.5 Pro Reasoning | o3 | Edge |
|---|---|---|---|
| Input price / 1M | $16.81 | $16.80 | B |
| Output price / 1M | $67.95 | $81.80 | A |
| Context window | 128,000 | 400,000 | B |
| Max output | 4,096 | 4,096 | Tie |
| Average score | 83.8 | 84.5 | B |
| Arena Elo | 1472.1 | 1449.0 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 2.5 Pro Reasoning wins 4, o3 wins 7, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Gemini 2.5 Pro Reasoning | o3 | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 86.8 | 86.9 | 0.1 | o3 |
| GPQA Diamond | 80.0 | 78.3 | 1.7 | Gemini 2.5 Pro Reasoning |
| SWE-bench Verified | 71.2 | 72.9 | 1.7 | o3 |
| HumanEval | 86.7 | 89.8 | 3.1 | o3 |
| MATH-500 | 87.9 | 87.9 | 0.0 | Tie |
| AIME 2025 | 84.2 | 84.4 | 0.2 | o3 |
| LiveCodeBench | 74.8 | 80.7 | 5.9 | o3 |
| IFEval | 90.8 | 88.7 | 2.1 | Gemini 2.5 Pro Reasoning |
| TruthfulQA | 84.0 | 84.6 | 0.6 | o3 |
| HellaSwag | 92.1 | 92.7 | 0.6 | o3 |
| MMMU | 82.8 | 82.3 | 0.5 | Gemini 2.5 Pro Reasoning |
| Arena Elo | 1472.1 | 1449.0 | 23.1 | Gemini 2.5 Pro Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, Gemini 2.5 Pro Reasoning costs about $29.59 per million tokens and o3 costs about $33.05. Gemini 2.5 Pro Reasoning is roughly 10% cheaper than o3. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
o3 has the larger context window at 400,000 tokens, compared with 128,000 for Gemini 2.5 Pro Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 2.5 Pro Reasoning wins 4, o3 wins 7, and 1 are tied. On the index average, o3 leads Gemini 2.5 Pro Reasoning by 0.7 points (84.5 versus 83.8).
The price picture favours Gemini 2.5 Pro Reasoning. The context picture favours o3. 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 o3 for quality-sensitive work and Gemini 2.5 Pro Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Gemini 2.5 Pro Reasoning if
- Unit cost matters and you want the cheaper blended price.
Choose o3 if
- You want the higher average benchmark score in this index.
- You need the larger 400,000-token context window.
FAQ
Is Gemini 2.5 Pro Reasoning better than o3?
On the index average, o3 leads Gemini 2.5 Pro Reasoning by 0.7 points (84.5 versus 83.8). The better choice depends on price, context and your task. Gemini 2.5 Pro Reasoning wins 4 benchmarks, o3 wins 7.
Which is cheaper, Gemini 2.5 Pro Reasoning or o3?
Gemini 2.5 Pro Reasoning is cheaper on a blended 3:1 basis at about $29.59 per million tokens, versus $33.05 for o3.
Which has the larger context window?
o3 has the larger context window at 400,000 tokens. Gemini 2.5 Pro Reasoning has 128,000 tokens.
Are these models open weights?
Gemini 2.5 Pro Reasoning is proprietary; o3 is proprietary.
Which should I choose for production?
If you need a single default, start with o3 for quality-sensitive work and Gemini 2.5 Pro Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.