Claude Sonnet 4.5 vs Gemini 3 Flash Pro: which model should you choose?
We compared Claude Sonnet 4.5 and Gemini 3 Flash Pro on price, context window and 12 benchmarks. Claude Sonnet 4.5 has the stronger average benchmark score; Claude Sonnet 4.5 is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5
Claude Sonnet 4.5 is a frontier model from Anthropic. It offers a 400,000-token context window, costs $17.84 per million input tokens and $70.50 per million output tokens, and averages 86.0 across the index's benchmark suite.
- Input
- $17.84 / 1M
- Output
- $70.50 / 1M
- Context
- 400,000
- Avg score
- 86.0
- Open weights
- No
Gemini 3 Flash Pro
Gemini 3 Flash Pro is a frontier model from Google DeepMind. It offers a 400,000-token context window, costs $17.71 per million input tokens and $86.50 per million output tokens, and averages 84.8 across the index's benchmark suite.
- Input
- $17.71 / 1M
- Output
- $86.50 / 1M
- Context
- 400,000
- Avg score
- 84.8
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 | Gemini 3 Flash Pro | Edge |
|---|---|---|---|
| Input price / 1M | $17.84 | $17.71 | B |
| Output price / 1M | $70.50 | $86.50 | A |
| Context window | 400,000 | 400,000 | Tie |
| Max output | 128,000 | 4,096 | A |
| Average score | 86.0 | 84.8 | A |
| Arena Elo | 1478.2 | 1469.2 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 wins 9, Gemini 3 Flash Pro wins 3, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 | Gemini 3 Flash Pro | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 88.0 | 87.0 | 1.0 | Claude Sonnet 4.5 |
| GPQA Diamond | 82.6 | 77.7 | 4.9 | Claude Sonnet 4.5 |
| SWE-bench Verified | 74.2 | 73.3 | 0.9 | Claude Sonnet 4.5 |
| HumanEval | 92.7 | 89.9 | 2.8 | Claude Sonnet 4.5 |
| MATH-500 | 87.0 | 91.8 | 4.8 | Gemini 3 Flash Pro |
| AIME 2025 | 86.3 | 79.9 | 6.4 | Claude Sonnet 4.5 |
| LiveCodeBench | 82.5 | 80.2 | 2.3 | Claude Sonnet 4.5 |
| IFEval | 91.1 | 92.8 | 1.7 | Gemini 3 Flash Pro |
| TruthfulQA | 87.2 | 86.2 | 1.0 | Claude Sonnet 4.5 |
| HellaSwag | 93.0 | 90.6 | 2.4 | Claude Sonnet 4.5 |
| MMMU | 80.9 | 83.0 | 2.1 | Gemini 3 Flash Pro |
| Arena Elo | 1478.2 | 1469.2 | 9.0 | Claude Sonnet 4.5 |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 costs about $31.00 per million tokens and Gemini 3 Flash Pro costs about $34.91. Claude Sonnet 4.5 is roughly 11% cheaper than Gemini 3 Flash Pro. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Both models list a 400,000-token context window. That is enough for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 wins 9, Gemini 3 Flash Pro wins 3, and 0 are tied. On the index average, Claude Sonnet 4.5 leads Gemini 3 Flash Pro by 1.2 points (86.0 versus 84.8).
The price picture favours Claude Sonnet 4.5. The context picture is effectively a tie. 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 Claude Sonnet 4.5 for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Sonnet 4.5 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 128,000-token output limit.
Choose Gemini 3 Flash Pro if
- You prefer Google DeepMind's tooling or already use it.
FAQ
Is Claude Sonnet 4.5 better than Gemini 3 Flash Pro?
On the index average, Claude Sonnet 4.5 leads Gemini 3 Flash Pro by 1.2 points (86.0 versus 84.8). The better choice depends on price, context and your task. Claude Sonnet 4.5 wins 9 benchmarks, Gemini 3 Flash Pro wins 3.
Which is cheaper, Claude Sonnet 4.5 or Gemini 3 Flash Pro?
Claude Sonnet 4.5 is cheaper on a blended 3:1 basis at about $31.00 per million tokens, versus $34.91 for Gemini 3 Flash Pro.
Which has the larger context window?
Both models list a 400,000-token context window.
Are these models open weights?
Claude Sonnet 4.5 is proprietary; Gemini 3 Flash Pro is proprietary.
Which should I choose for production?
If you need a single default, start with Claude Sonnet 4.5 for quality-sensitive work, and check whether its price holds at your expected volume before committing.