Claude Sonnet 4.5 vs GPT-5.1 Vision: which model should you choose?
We compared Claude Sonnet 4.5 and GPT-5.1 Vision 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
GPT-5.1 Vision
GPT-5.1 Vision is a frontier model from OpenAI. It offers a 400,000-token context window, costs $17.76 per million input tokens and $80.59 per million output tokens, and averages 84.8 across the index's benchmark suite.
- Input
- $17.76 / 1M
- Output
- $80.59 / 1M
- Context
- 400,000
- Avg score
- 84.8
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 | GPT-5.1 Vision | Edge |
|---|---|---|---|
| Input price / 1M | $17.84 | $17.76 | B |
| Output price / 1M | $70.50 | $80.59 | A |
| Context window | 400,000 | 400,000 | Tie |
| Max output | 128,000 | 16,384 | A |
| Average score | 86.0 | 84.8 | A |
| Arena Elo | 1478.2 | 1462.4 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 wins 9, GPT-5.1 Vision wins 3, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 | GPT-5.1 Vision | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 88.0 | 85.5 | 2.5 | Claude Sonnet 4.5 |
| GPQA Diamond | 82.6 | 78.7 | 3.9 | Claude Sonnet 4.5 |
| SWE-bench Verified | 74.2 | 73.6 | 0.6 | Claude Sonnet 4.5 |
| HumanEval | 92.7 | 89.6 | 3.1 | Claude Sonnet 4.5 |
| MATH-500 | 87.0 | 89.1 | 2.1 | GPT-5.1 Vision |
| AIME 2025 | 86.3 | 82.4 | 3.9 | Claude Sonnet 4.5 |
| LiveCodeBench | 82.5 | 77.8 | 4.7 | Claude Sonnet 4.5 |
| IFEval | 91.1 | 92.7 | 1.6 | GPT-5.1 Vision |
| TruthfulQA | 87.2 | 86.9 | 0.3 | Claude Sonnet 4.5 |
| HellaSwag | 93.0 | 92.1 | 0.9 | Claude Sonnet 4.5 |
| MMMU | 80.9 | 83.9 | 3.0 | GPT-5.1 Vision |
| Arena Elo | 1478.2 | 1462.4 | 15.8 | 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 GPT-5.1 Vision costs about $33.47. Claude Sonnet 4.5 is roughly 7% cheaper than GPT-5.1 Vision. 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, GPT-5.1 Vision wins 3, and 0 are tied. On the index average, Claude Sonnet 4.5 leads GPT-5.1 Vision 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 GPT-5.1 Vision if
- You prefer OpenAI's tooling or already use it.
FAQ
Is Claude Sonnet 4.5 better than GPT-5.1 Vision?
On the index average, Claude Sonnet 4.5 leads GPT-5.1 Vision 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, GPT-5.1 Vision wins 3.
Which is cheaper, Claude Sonnet 4.5 or GPT-5.1 Vision?
Claude Sonnet 4.5 is cheaper on a blended 3:1 basis at about $31.00 per million tokens, versus $33.47 for GPT-5.1 Vision.
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; GPT-5.1 Vision 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.