Gemini 3 Flash Reasoning vs o3: which model should you choose?
We compared Gemini 3 Flash Reasoning and o3 on price, context window and 12 benchmarks. o3 has the stronger average benchmark score; Gemini 3 Flash Reasoning is cheaper on a blended 3:1 basis.
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
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 3 Flash Reasoning | o3 | Edge |
|---|---|---|---|
| Input price / 1M | $17.05 | $16.80 | B |
| Output price / 1M | $66.77 | $81.80 | A |
| Context window | 128,000 | 400,000 | B |
| Max output | 32,768 | 4,096 | A |
| Average score | 83.7 | 84.5 | B |
| Arena Elo | 1446.9 | 1449.0 | B |
| Open weights | No | No | Tie |
Benchmark comparison
Gemini 3 Flash Reasoning wins 4, o3 wins 8, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Gemini 3 Flash Reasoning | o3 | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.2 | 86.9 | 0.3 | Gemini 3 Flash Reasoning |
| GPQA Diamond | 81.8 | 78.3 | 3.5 | Gemini 3 Flash Reasoning |
| SWE-bench Verified | 72.5 | 72.9 | 0.4 | o3 |
| HumanEval | 86.9 | 89.8 | 2.9 | o3 |
| MATH-500 | 86.2 | 87.9 | 1.7 | o3 |
| AIME 2025 | 79.4 | 84.4 | 5.0 | o3 |
| LiveCodeBench | 77.7 | 80.7 | 3.0 | o3 |
| IFEval | 90.2 | 88.7 | 1.5 | Gemini 3 Flash Reasoning |
| TruthfulQA | 86.6 | 84.6 | 2.0 | Gemini 3 Flash Reasoning |
| HellaSwag | 92.2 | 92.7 | 0.5 | o3 |
| MMMU | 79.8 | 82.3 | 2.5 | o3 |
| Arena Elo | 1446.9 | 1449.0 | 2.1 | o3 |
Price analysis
On a blended 3:1 input-to-output basis, Gemini 3 Flash Reasoning costs about $29.48 per million tokens and o3 costs about $33.05. Gemini 3 Flash Reasoning is roughly 11% 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 3 Flash Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Gemini 3 Flash Reasoning wins 4, o3 wins 8, and 0 are tied. On the index average, o3 leads Gemini 3 Flash Reasoning by 0.8 points (84.5 versus 83.7).
The price picture favours Gemini 3 Flash 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 3 Flash Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Gemini 3 Flash Reasoning if
- Unit cost matters and you want the cheaper blended price.
- You need the larger 32,768-token output limit.
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 3 Flash Reasoning better than o3?
On the index average, o3 leads Gemini 3 Flash Reasoning by 0.8 points (84.5 versus 83.7). The better choice depends on price, context and your task. Gemini 3 Flash Reasoning wins 4 benchmarks, o3 wins 8.
Which is cheaper, Gemini 3 Flash Reasoning or o3?
Gemini 3 Flash Reasoning is cheaper on a blended 3:1 basis at about $29.48 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 3 Flash Reasoning has 128,000 tokens.
Are these models open weights?
Gemini 3 Flash 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 3 Flash Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.