Claude Opus 4.5 vs Grok 4 Reasoning: which model should you choose?
We compared Claude Opus 4.5 and Grok 4 Reasoning on price, context window and 12 benchmarks. Grok 4 Reasoning 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
Grok 4 Reasoning
Grok 4 Reasoning is a frontier model from xAI. It offers a 2,000,000-token context window, costs $19.67 per million input tokens and $93.29 per million output tokens, and averages 87.8 across the index's benchmark suite.
- Input
- $19.67 / 1M
- Output
- $93.29 / 1M
- Context
- 2,000,000
- Avg score
- 87.8
- Open weights
- No
Specification comparison
| Spec | Claude Opus 4.5 | Grok 4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.42 | $19.67 | A |
| Output price / 1M | $75.27 | $93.29 | A |
| Context window | 400,000 | 2,000,000 | B |
| Max output | 4,096 | 65,536 | B |
| Average score | 87.7 | 87.8 | B |
| Arena Elo | 1491.2 | 1487.6 | A |
| Open weights | No | No | Tie |
Benchmark comparison
Claude Opus 4.5 wins 3, Grok 4 Reasoning wins 9, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | Claude Opus 4.5 | Grok 4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 87.0 | 88.5 | 1.5 | Grok 4 Reasoning |
| GPQA Diamond | 81.7 | 81.9 | 0.2 | Grok 4 Reasoning |
| SWE-bench Verified | 77.1 | 78.0 | 0.9 | Grok 4 Reasoning |
| HumanEval | 93.7 | 93.8 | 0.1 | Grok 4 Reasoning |
| MATH-500 | 93.7 | 94.4 | 0.7 | Grok 4 Reasoning |
| AIME 2025 | 89.8 | 85.6 | 4.2 | Claude Opus 4.5 |
| LiveCodeBench | 85.0 | 85.1 | 0.1 | Grok 4 Reasoning |
| IFEval | 92.5 | 93.4 | 0.9 | Grok 4 Reasoning |
| TruthfulQA | 88.1 | 89.4 | 1.3 | Grok 4 Reasoning |
| HellaSwag | 92.4 | 95.2 | 2.8 | Grok 4 Reasoning |
| MMMU | 84.2 | 80.8 | 3.4 | Claude Opus 4.5 |
| Arena Elo | 1491.2 | 1487.6 | 3.6 | 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 Grok 4 Reasoning costs about $38.08. Claude Opus 4.5 is roughly 12% cheaper than Grok 4 Reasoning. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Grok 4 Reasoning has the larger context window at 2,000,000 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 3, Grok 4 Reasoning wins 9, and 0 are tied. On the index average, Grok 4 Reasoning leads Claude Opus 4.5 by 0.1 points (87.8 versus 87.7).
The price picture favours Claude Opus 4.5. The context picture favours Grok 4 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 Grok 4 Reasoning for quality-sensitive work and Claude Opus 4.5 for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose Claude Opus 4.5 if
- Unit cost matters and you want the cheaper blended price.
Choose Grok 4 Reasoning 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 65,536-token output limit.
FAQ
Is Claude Opus 4.5 better than Grok 4 Reasoning?
On the index average, Grok 4 Reasoning leads Claude Opus 4.5 by 0.1 points (87.8 versus 87.7). The better choice depends on price, context and your task. Claude Opus 4.5 wins 3 benchmarks, Grok 4 Reasoning wins 9.
Which is cheaper, Claude Opus 4.5 or Grok 4 Reasoning?
Claude Opus 4.5 is cheaper on a blended 3:1 basis at about $33.38 per million tokens, versus $38.08 for Grok 4 Reasoning.
Which has the larger context window?
Grok 4 Reasoning has the larger context window at 2,000,000 tokens. Claude Opus 4.5 has 400,000 tokens.
Are these models open weights?
Claude Opus 4.5 is proprietary; Grok 4 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with Grok 4 Reasoning for quality-sensitive work and Claude Opus 4.5 for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.