GPT-5.1 vs Grok 4 Pro: which model should you choose?
We compared GPT-5.1 and Grok 4 Pro on price, context window and 12 benchmarks. GPT-5.1 has the stronger average benchmark score; GPT-5.1 is cheaper on a blended 3:1 basis.
GPT-5.1
GPT-5.1 is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.01 per million input tokens and $69.84 per million output tokens, and averages 86.0 across the index's benchmark suite.
- Input
- $19.01 / 1M
- Output
- $69.84 / 1M
- Context
- 2,000,000
- Avg score
- 86.0
- Open weights
- No
Grok 4 Pro
Grok 4 Pro is a frontier model from xAI. It offers a 1,000,000-token context window, costs $19.00 per million input tokens and $77.72 per million output tokens, and averages 85.4 across the index's benchmark suite.
- Input
- $19.00 / 1M
- Output
- $77.72 / 1M
- Context
- 1,000,000
- Avg score
- 85.4
- Open weights
- No
Specification comparison
| Spec | GPT-5.1 | Grok 4 Pro | Edge |
|---|---|---|---|
| Input price / 1M | $19.01 | $19.00 | B |
| Output price / 1M | $69.84 | $77.72 | A |
| Context window | 2,000,000 | 1,000,000 | A |
| Max output | 128,000 | 128,000 | Tie |
| Average score | 86.0 | 85.4 | A |
| Arena Elo | 1462.5 | 1487.5 | B |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 wins 7, Grok 4 Pro wins 5, and 0 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 | Grok 4 Pro | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 86.1 | 84.9 | 1.2 | GPT-5.1 |
| GPQA Diamond | 82.3 | 79.2 | 3.1 | GPT-5.1 |
| SWE-bench Verified | 76.1 | 74.7 | 1.4 | GPT-5.1 |
| HumanEval | 90.6 | 89.7 | 0.9 | GPT-5.1 |
| MATH-500 | 90.5 | 92.3 | 1.8 | Grok 4 Pro |
| AIME 2025 | 85.6 | 85.4 | 0.2 | GPT-5.1 |
| LiveCodeBench | 78.9 | 77.8 | 1.1 | GPT-5.1 |
| IFEval | 90.9 | 91.3 | 0.4 | Grok 4 Pro |
| TruthfulQA | 89.2 | 86.0 | 3.2 | GPT-5.1 |
| HellaSwag | 92.2 | 92.8 | 0.6 | Grok 4 Pro |
| MMMU | 83.3 | 84.9 | 1.6 | Grok 4 Pro |
| Arena Elo | 1462.5 | 1487.5 | 25.0 | Grok 4 Pro |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 costs about $31.72 per million tokens and Grok 4 Pro costs about $33.68. GPT-5.1 is roughly 6% cheaper than Grok 4 Pro. At high volume, that gap compounds quickly, so price should carry real weight unless the quality difference is decisive.
GPT-5.1 has the larger context window at 2,000,000 tokens, compared with 1,000,000 for Grok 4 Pro. That matters for long documents, large codebases and multi-step agent traces.
Verdict
Across 12 shared benchmarks, GPT-5.1 wins 7, Grok 4 Pro wins 5, and 0 are tied. On the index average, GPT-5.1 leads Grok 4 Pro by 0.6 points (86.0 versus 85.4).
The price picture favours GPT-5.1. The context picture favours GPT-5.1. 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 for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose GPT-5.1 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 2,000,000-token context window.
Choose Grok 4 Pro if
- You prefer xAI's tooling or already use it.
FAQ
Is GPT-5.1 better than Grok 4 Pro?
On the index average, GPT-5.1 leads Grok 4 Pro by 0.6 points (86.0 versus 85.4). The better choice depends on price, context and your task. GPT-5.1 wins 7 benchmarks, Grok 4 Pro wins 5.
Which is cheaper, GPT-5.1 or Grok 4 Pro?
GPT-5.1 is cheaper on a blended 3:1 basis at about $31.72 per million tokens, versus $33.68 for Grok 4 Pro.
Which has the larger context window?
GPT-5.1 has the larger context window at 2,000,000 tokens. Grok 4 Pro has 1,000,000 tokens.
Are these models open weights?
GPT-5.1 is proprietary; Grok 4 Pro is proprietary.
Which should I choose for production?
If you need a single default, start with GPT-5.1 for quality-sensitive work, and check whether its price holds at your expected volume before committing.