Claude Sonnet 4.5 Reasoning vs o4 Reasoning: which model should you choose?
We compared Claude Sonnet 4.5 Reasoning and o4 Reasoning on price, context window and 12 benchmarks. Claude Sonnet 4.5 Reasoning 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
o4 Reasoning
o4 Reasoning is a frontier model from OpenAI. It offers a 1,000,000-token context window, costs $19.69 per million input tokens and $103.53 per million output tokens, and averages 87.5 across the index's benchmark suite.
- Input
- $19.69 / 1M
- Output
- $103.53 / 1M
- Context
- 1,000,000
- Avg score
- 87.5
- Open weights
- No
Specification comparison
| Spec | Claude Sonnet 4.5 Reasoning | o4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.48 | $19.69 | A |
| Output price / 1M | $68.20 | $103.53 | A |
| Context window | 400,000 | 1,000,000 | B |
| Max output | 8,192 | 128,000 | B |
| Average score | 87.7 | 87.5 | A |
| Arena Elo | 1486.5 | 1472.2 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Sonnet 4.5 Reasoning wins 8, o4 Reasoning wins 4, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Sonnet 4.5 Reasoning | o4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.6 | 86.1 | 1.5 | Claude Sonnet 4.5 Reasoning |
| GPQA Diamond | 85.2 | 84.0 | 1.2 | Claude Sonnet 4.5 Reasoning |
| SWE-bench Verified | 79.6 | 76.4 | 3.2 | Claude Sonnet 4.5 Reasoning |
| HumanEval | 90.3 | 90.2 | 0.1 | Claude Sonnet 4.5 Reasoning |
| MATH-500 | 89.7 | 94.8 | 5.1 | o4 Reasoning |
| AIME 2025 | 87.3 | 90.3 | 3.0 | o4 Reasoning |
| LiveCodeBench | 85.1 | 83.4 | 1.7 | Claude Sonnet 4.5 Reasoning |
| IFEval | 91.9 | 94.5 | 2.6 | o4 Reasoning |
| TruthfulQA | 87.6 | 89.0 | 1.4 | o4 Reasoning |
| HellaSwag | 95.2 | 92.4 | 2.8 | Claude Sonnet 4.5 Reasoning |
| MMMU | 85.2 | 81.8 | 3.4 | Claude Sonnet 4.5 Reasoning |
| Arena Elo | 1486.5 | 1472.2 | 14.3 | 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 o4 Reasoning costs about $40.65. Claude Sonnet 4.5 Reasoning is roughly 22% cheaper than o4 Reasoning. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
o4 Reasoning has the larger context window at 1,000,000 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 8, o4 Reasoning wins 4, and 0 are tied. On the index average, Claude Sonnet 4.5 Reasoning leads o4 Reasoning by 0.2 points (87.7 versus 87.5).
The price picture favours Claude Sonnet 4.5 Reasoning. The context picture favours o4 Reasoning. 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 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Sonnet 4.5 Reasoning if
- You want the higher average benchmark score in this index.
- Unit cost matters and you want the cheaper blended price.
Choose o4 Reasoning if
- You need the larger 1,000,000-token context window.
- You need the larger 128,000-token output limit.
FAQ
Is Claude Sonnet 4.5 Reasoning better than o4 Reasoning?
On the index average, Claude Sonnet 4.5 Reasoning leads o4 Reasoning by 0.2 points (87.7 versus 87.5). The better choice depends on price, context and your task. Claude Sonnet 4.5 Reasoning wins 8 benchmarks, o4 Reasoning wins 4.
Which is cheaper, Claude Sonnet 4.5 Reasoning or o4 Reasoning?
Claude Sonnet 4.5 Reasoning is cheaper on a blended 3:1 basis at about $31.66 per million tokens, versus $40.65 for o4 Reasoning.
Which has the larger context window?
o4 Reasoning has the larger context window at 1,000,000 tokens. Claude Sonnet 4.5 Reasoning has 400,000 tokens.
Are these models open weights?
Claude Sonnet 4.5 Reasoning is proprietary; o4 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with Claude Sonnet 4.5 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.