Claude Opus 4.5 vs o4 Reasoning: which model should you choose?
We compared Claude Opus 4.5 and o4 Reasoning on price, context window and 12 benchmarks. Claude Opus 4.5 has the stronger average benchmark score; Claude Opus 4.5 is cheaper on a blended 3:1 basis.
Claude Opus 4.5
Claude Opus 4.5 is a frontier model from Anthropic. It offers a 400,000-token context window, costs $19.42 per million input tokens and $75.27 per million output tokens, and averages 87.7 across the index's benchmark suite.
- Input
- $19.42 / 1M
- Output
- $75.27 / 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 Opus 4.5 | o4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.42 | $19.69 | A |
| Output price / 1M | $75.27 | $103.53 | A |
| Context window | 400,000 | 1,000,000 | B |
| Max output | 4,096 | 128,000 | B |
| Average score | 87.7 | 87.5 | A |
| Arena Elo | 1491.2 | 1472.2 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Opus 4.5 wins 6, o4 Reasoning wins 5, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Opus 4.5 | o4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.0 | 86.1 | 0.9 | Claude Opus 4.5 |
| GPQA Diamond | 81.7 | 84.0 | 2.3 | o4 Reasoning |
| SWE-bench Verified | 77.1 | 76.4 | 0.7 | Claude Opus 4.5 |
| HumanEval | 93.7 | 90.2 | 3.5 | Claude Opus 4.5 |
| MATH-500 | 93.7 | 94.8 | 1.1 | o4 Reasoning |
| AIME 2025 | 89.8 | 90.3 | 0.5 | o4 Reasoning |
| LiveCodeBench | 85.0 | 83.4 | 1.6 | Claude Opus 4.5 |
| IFEval | 92.5 | 94.5 | 2.0 | o4 Reasoning |
| TruthfulQA | 88.1 | 89.0 | 0.9 | o4 Reasoning |
| HellaSwag | 92.4 | 92.4 | 0.0 | Tie |
| MMMU | 84.2 | 81.8 | 2.4 | Claude Opus 4.5 |
| Arena Elo | 1491.2 | 1472.2 | 19.0 | Claude Opus 4.5 |
Price analysis
On a blended 3:1 input-to-output basis, Claude Opus 4.5 costs about $33.38 per million tokens and o4 Reasoning costs about $40.65. Claude Opus 4.5 is roughly 18% 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 Opus 4.5. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, Claude Opus 4.5 wins 6, o4 Reasoning wins 5, and 1 are tied. On the index average, Claude Opus 4.5 leads o4 Reasoning by 0.2 points (87.7 versus 87.5).
The price picture favours Claude Opus 4.5. 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 Opus 4.5 for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose Claude Opus 4.5 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 Opus 4.5 better than o4 Reasoning?
On the index average, Claude Opus 4.5 leads o4 Reasoning by 0.2 points (87.7 versus 87.5). The better choice depends on price, context and your task. Claude Opus 4.5 wins 6 benchmarks, o4 Reasoning wins 5.
Which is cheaper, Claude Opus 4.5 or o4 Reasoning?
Claude Opus 4.5 is cheaper on a blended 3:1 basis at about $33.38 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 Opus 4.5 has 400,000 tokens.
Are these models open weights?
Claude Opus 4.5 is proprietary; o4 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with Claude Opus 4.5 for quality-sensitive work, and check whether its price holds at your expected volume before committing.