GPT-5.1 Max vs Grok 4 Reasoning: which model should you choose?
We compared GPT-5.1 Max and Grok 4 Reasoning on price, context window and 12 benchmarks. GPT-5.1 Max has the stronger average benchmark score; Grok 4 Reasoning is cheaper on a blended 3:1 basis.
GPT-5.1 Max
GPT-5.1 Max is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $20.50 per million input tokens and $103.98 per million output tokens, and averages 87.9 across the index's benchmark suite.
- Input
- $20.50 / 1M
- Output
- $103.98 / 1M
- Context
- 2,000,000
- Avg score
- 87.9
- 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 | GPT-5.1 Max | Grok 4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $20.50 | $19.67 | B |
| Output price / 1M | $103.98 | $93.29 | B |
| Context window | 2,000,000 | 2,000,000 | Tie |
| Max output | 8,192 | 65,536 | B |
| Average score | 87.9 | 87.8 | A |
| Arena Elo | 1478.2 | 1487.6 | B |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 Max wins 5, Grok 4 Reasoning wins 7, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 Max | Grok 4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 91.3 | 88.5 | 2.8 | GPT-5.1 Max |
| GPQA Diamond | 86.4 | 81.9 | 4.5 | GPT-5.1 Max |
| SWE-bench Verified | 75.6 | 78.0 | 2.4 | Grok 4 Reasoning |
| HumanEval | 92.2 | 93.8 | 1.6 | Grok 4 Reasoning |
| MATH-500 | 91.3 | 94.4 | 3.1 | Grok 4 Reasoning |
| AIME 2025 | 88.8 | 85.6 | 3.2 | GPT-5.1 Max |
| LiveCodeBench | 80.2 | 85.1 | 4.9 | Grok 4 Reasoning |
| IFEval | 92.2 | 93.4 | 1.2 | Grok 4 Reasoning |
| TruthfulQA | 91.1 | 89.4 | 1.7 | GPT-5.1 Max |
| HellaSwag | 93.1 | 95.2 | 2.1 | Grok 4 Reasoning |
| MMMU | 85.1 | 80.8 | 4.3 | GPT-5.1 Max |
| Arena Elo | 1478.2 | 1487.6 | 9.4 | Grok 4 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 Max costs about $41.37 per million tokens and Grok 4 Reasoning costs about $38.08. Grok 4 Reasoning is roughly 8% cheaper than GPT-5.1 Max. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
Both models list a 2,000,000-token context window. That is enough for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, GPT-5.1 Max wins 5, Grok 4 Reasoning wins 7, and 0 are tied. On the index average, GPT-5.1 Max leads Grok 4 Reasoning by 0.1 points (87.9 versus 87.8).
The price picture favours Grok 4 Reasoning. 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 GPT-5.1 Max for quality-sensitive work and Grok 4 Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose GPT-5.1 Max if
- You want the higher average benchmark score in this index.
Choose Grok 4 Reasoning if
- Unit cost matters and you want the cheaper blended price.
- You need the larger 65,536-token output limit.
FAQ
Is GPT-5.1 Max better than Grok 4 Reasoning?
On the index average, GPT-5.1 Max leads Grok 4 Reasoning by 0.1 points (87.9 versus 87.8). The better choice depends on price, context and your task. GPT-5.1 Max wins 5 benchmarks, Grok 4 Reasoning wins 7.
Which is cheaper, GPT-5.1 Max or Grok 4 Reasoning?
Grok 4 Reasoning is cheaper on a blended 3:1 basis at about $38.08 per million tokens, versus $41.37 for GPT-5.1 Max.
Which has the larger context window?
Both models list a 2,000,000-token context window.
Are these models open weights?
GPT-5.1 Max is proprietary; Grok 4 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 Max for quality-sensitive work and Grok 4 Reasoning for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.