GPT-5.1 Turbo vs Grok 4 Reasoning: which model should you choose?
We compared GPT-5.1 Turbo and Grok 4 Reasoning on price, context window and 12 benchmarks. Grok 4 Reasoning has the stronger average benchmark score; GPT-5.1 Turbo is cheaper on a blended 3:1 basis.
GPT-5.1 Turbo
GPT-5.1 Turbo is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.19 per million input tokens and $89.83 per million output tokens, and averages 86.1 across the index's benchmark suite.
- Input
- $19.19 / 1M
- Output
- $89.83 / 1M
- Context
- 2,000,000
- Avg score
- 86.1
- 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 Turbo | Grok 4 Reasoning | Edge |
|---|---|---|---|
| Input price / 1M | $19.19 | $19.67 | A |
| Output price / 1M | $89.83 | $93.29 | A |
| Context window | 2,000,000 | 2,000,000 | Tie |
| Max output | 128,000 | 65,536 | A |
| Average score | 86.1 | 87.8 | B |
| Arena Elo | 1482.0 | 1487.6 | B |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 Turbo wins 0, Grok 4 Reasoning wins 11, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 Turbo | Grok 4 Reasoning | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 85.2 | 88.5 | 3.3 | Grok 4 Reasoning |
| GPQA Diamond | 81.3 | 81.9 | 0.6 | Grok 4 Reasoning |
| SWE-bench Verified | 74.7 | 78.0 | 3.3 | Grok 4 Reasoning |
| HumanEval | 91.5 | 93.8 | 2.3 | Grok 4 Reasoning |
| MATH-500 | 91.4 | 94.4 | 3.0 | Grok 4 Reasoning |
| AIME 2025 | 84.7 | 85.6 | 0.9 | Grok 4 Reasoning |
| LiveCodeBench | 84.6 | 85.1 | 0.5 | Grok 4 Reasoning |
| IFEval | 93.4 | 93.4 | 0.0 | Tie |
| TruthfulQA | 89.2 | 89.4 | 0.2 | Grok 4 Reasoning |
| HellaSwag | 91.3 | 95.2 | 3.9 | Grok 4 Reasoning |
| MMMU | 79.7 | 80.8 | 1.1 | Grok 4 Reasoning |
| Arena Elo | 1482.0 | 1487.6 | 5.6 | Grok 4 Reasoning |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 Turbo costs about $36.85 per million tokens and Grok 4 Reasoning costs about $38.08. GPT-5.1 Turbo is roughly 3% cheaper than Grok 4 Reasoning. 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 Turbo wins 0, Grok 4 Reasoning wins 11, and 1 are tied. On the index average, Grok 4 Reasoning leads GPT-5.1 Turbo by 1.7 points (87.8 versus 86.1).
The price picture favours GPT-5.1 Turbo. 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 Grok 4 Reasoning for quality-sensitive work and GPT-5.1 Turbo for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.
Choose GPT-5.1 Turbo if
- 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 want the higher average benchmark score in this index.
FAQ
Is GPT-5.1 Turbo better than Grok 4 Reasoning?
On the index average, Grok 4 Reasoning leads GPT-5.1 Turbo by 1.7 points (87.8 versus 86.1). The better choice depends on price, context and your task. GPT-5.1 Turbo wins 0 benchmarks, Grok 4 Reasoning wins 11.
Which is cheaper, GPT-5.1 Turbo or Grok 4 Reasoning?
GPT-5.1 Turbo is cheaper on a blended 3:1 basis at about $36.85 per million tokens, versus $38.08 for Grok 4 Reasoning.
Which has the larger context window?
Both models list a 2,000,000-token context window.
Are these models open weights?
GPT-5.1 Turbo 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 GPT-5.1 Turbo for high-volume, well-scoped tasks. Run both on a sample of your own traffic before locking in a choice.