GPT-5.1 Reasoning vs Grok 4 Reasoning: which model should you choose?
We compared GPT-5.1 Reasoning and Grok 4 Reasoning on price, context window and 12 benchmarks. GPT-5.1 Reasoning has the stronger average benchmark score; GPT-5.1 Reasoning is cheaper on a blended 3:1 basis.
GPT-5.1 Reasoning
GPT-5.1 Reasoning is a frontier model from OpenAI. It offers a 400,000-token context window, costs $20.27 per million input tokens and $82.11 per million output tokens, and averages 88.3 across the index's benchmark suite.
- Input
- $20.27 / 1M
- Output
- $82.11 / 1M
- Context
- 400,000
- Avg score
- 88.3
- 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 Reasoning | Grok 4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $20.27 | $19.67 | B |
| Output price / 1M | $82.11 | $93.29 | A |
| Context window | 400,000 | 2,000,000 | B |
| Max output | 128,000 | 65,536 | A |
| Average score | 88.3 | 87.8 | A |
| Arena Elo | 1485.9 | 1487.6 | B |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 Reasoning wins 6, Grok 4 Reasoning wins 6, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 Reasoning | Grok 4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 90.0 | 88.5 | 1.5 | GPT-5.1 Reasoning |
| GPQA Diamond | 85.6 | 81.9 | 3.7 | GPT-5.1 Reasoning |
| SWE-bench Verified | 76.0 | 78.0 | 2.0 | Grok 4 Reasoning |
| HumanEval | 92.9 | 93.8 | 0.9 | Grok 4 Reasoning |
| MATH-500 | 95.9 | 94.4 | 1.5 | GPT-5.1 Reasoning |
| AIME 2025 | 85.0 | 85.6 | 0.6 | Grok 4 Reasoning |
| LiveCodeBench | 80.9 | 85.1 | 4.2 | Grok 4 Reasoning |
| IFEval | 94.6 | 93.4 | 1.2 | GPT-5.1 Reasoning |
| TruthfulQA | 90.0 | 89.4 | 0.6 | GPT-5.1 Reasoning |
| HellaSwag | 94.4 | 95.2 | 0.8 | Grok 4 Reasoning |
| MMMU | 86.2 | 80.8 | 5.4 | GPT-5.1 Reasoning |
| Arena Elo | 1485.9 | 1487.6 | 1.7 | Grok 4 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 Reasoning costs about $35.73 per million tokens and Grok 4 Reasoning costs about $38.08. GPT-5.1 Reasoning is roughly 6% 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 GPT-5.1 Reasoning. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, GPT-5.1 Reasoning wins 6, Grok 4 Reasoning wins 6, and 0 are tied. On the index average, GPT-5.1 Reasoning leads Grok 4 Reasoning by 0.5 points (88.3 versus 87.8).
The price picture favours GPT-5.1 Reasoning. 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 GPT-5.1 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose GPT-5.1 Reasoning if
- You want the higher average benchmark score in this index.
- Unit cost matters and you want the cheaper blended price.
- You need the larger 128,000-token output limit.
Choose Grok 4 Reasoning if
- You need the larger 2,000,000-token context window.
FAQ
Is GPT-5.1 Reasoning better than Grok 4 Reasoning?
On the index average, GPT-5.1 Reasoning leads Grok 4 Reasoning by 0.5 points (88.3 versus 87.8). The better choice depends on price, context and your task. GPT-5.1 Reasoning wins 6 benchmarks, Grok 4 Reasoning wins 6.
Which is cheaper, GPT-5.1 Reasoning or Grok 4 Reasoning?
GPT-5.1 Reasoning is cheaper on a blended 3:1 basis at about $35.73 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. GPT-5.1 Reasoning has 400,000 tokens.
Are these models open weights?
GPT-5.1 Reasoning is proprietary; Grok 4 Reasoning is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 Reasoning for quality-sensitive work, and check whether its price holds at your expected volume before committing.