Claude Sonnet 4.5 Reasoning vs GPT-5.2: which model should you choose?
We compared Claude Sonnet 4.5 Reasoning and GPT-5.2 on price, context window and 12 benchmarks. GPT-5.2 has the stronger average benchmark score; Claude Sonnet 4.5 Reasoning is cheaper on a blended 3:1 basis.
Claude Sonnet 4.5 Reasoning
Claude Sonnet 4.5 Reasoning is a frontier model from Anthropic. It offers a 400,000-token context window, costs $19.48 per million input tokens and $68.20 per million output tokens, and averages 87.7 across the index's benchmark suite.
- Input
- $19.48 / 1M
- Output
- $68.20 / 1M
- Context
- 400,000
- Avg score
- 87.7
- Open weights
- No
GPT-5.2
GPT-5.2 is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.71 per million input tokens and $85.71 per million output tokens, and averages 88.0 across the index's benchmark suite.
- Input
- $19.71 / 1M
- Output
- $85.71 / 1M
- Context
- 2,000,000
- Avg score
- 88.0
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 Reasoning | GPT-5.2 | Edge |
|---|---|---|---|
| Input price / 1M | $19.48 | $19.71 | A |
| Output price / 1M | $68.20 | $85.71 | A |
| Context window | 400,000 | 2,000,000 | B |
| Max output | 8,192 | 16,384 | B |
| Average score | 87.7 | 88.0 | B |
| Arena Elo | 1486.5 | 1478.0 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Reasoning wins 4, GPT-5.2 wins 8, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Reasoning | GPT-5.2 | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.6 | 89.9 | 2.3 | GPT-5.2 |
| GPQA Diamond | 85.2 | 84.9 | 0.3 | Claude Sonnet 4.5 Reasoning |
| SWE-bench Verified | 79.6 | 80.2 | 0.6 | GPT-5.2 |
| HumanEval | 90.3 | 91.0 | 0.7 | GPT-5.2 |
| MATH-500 | 89.7 | 90.6 | 0.9 | GPT-5.2 |
| AIME 2025 | 87.3 | 90.6 | 3.3 | GPT-5.2 |
| LiveCodeBench | 85.1 | 79.7 | 5.4 | Claude Sonnet 4.5 Reasoning |
| IFEval | 91.9 | 93.6 | 1.7 | GPT-5.2 |
| TruthfulQA | 87.6 | 89.7 | 2.1 | GPT-5.2 |
| HellaSwag | 95.2 | 92.6 | 2.6 | Claude Sonnet 4.5 Reasoning |
| MMMU | 85.2 | 85.3 | 0.1 | GPT-5.2 |
| Arena Elo | 1486.5 | 1478.0 | 8.5 | Claude Sonnet 4.5 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, Claude Sonnet 4.5 Reasoning costs about $31.66 per million tokens and GPT-5.2 costs about $36.21. Claude Sonnet 4.5 Reasoning is roughly 13% cheaper than GPT-5.2. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
GPT-5.2 has the larger context window at 2,000,000 tokens, compared with 400,000 for Claude Sonnet 4.5 Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Sonnet 4.5 Reasoning wins 4, GPT-5.2 wins 8, and 0 are tied. On the index average, GPT-5.2 leads Claude Sonnet 4.5 Reasoning by 0.3 points (88.0 versus 87.7).
The price picture favours Claude Sonnet 4.5 Reasoning. The context picture favours GPT-5.2. 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 GPT-5.2 for quality-sensitive work and Claude Sonnet 4.5 Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Claude Sonnet 4.5 Reasoning if
- Unit cost matters and you want the cheaper blended price.
Choose GPT-5.2 if
- You want the higher average benchmark score in this index.
- You need the larger 2,000,000-token context window.
- You need the larger 16,384-token output limit.
FAQ
Is Claude Sonnet 4.5 Reasoning better than GPT-5.2?
On the index average, GPT-5.2 leads Claude Sonnet 4.5 Reasoning by 0.3 points (88.0 versus 87.7). The better choice depends on price, context and your task. Claude Sonnet 4.5 Reasoning wins 4 benchmarks, GPT-5.2 wins 8.
Which is cheaper, Claude Sonnet 4.5 Reasoning or GPT-5.2?
Claude Sonnet 4.5 Reasoning is cheaper on a blended 3:1 basis at about $31.66 per million tokens, versus $36.21 for GPT-5.2.
Which has the larger context window?
GPT-5.2 has the larger context window at 2,000,000 tokens. Claude Sonnet 4.5 Reasoning has 400,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Reasoning is proprietary; GPT-5.2 is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.2 for quality-sensitive work and Claude Sonnet 4.5 Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.