GPT-5.1 Turbo vs o4 Turbo: which model should you choose?
We compared GPT-5.1 Turbo and o4 Turbo on price, context window and 12 benchmarks. o4 Turbo has the stronger average benchmark score; o4 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
o4 Turbo
o4 Turbo is a frontier model from OpenAI. It offers a 2,000,000-token context window, costs $19.34 per million input tokens and $82.19 per million output tokens, and averages 86.6 across the index's benchmark suite.
- Input
- $19.34 / 1M
- Output
- $82.19 / 1M
- Context
- 2,000,000
- Avg score
- 86.6
- Open weights
- No
Specification comparison
| Spec | GPT-5.1 Turbo | o4 Turbo | Edge |
|---|---|---|---|
| Input price / 1M | $19.19 | $19.34 | A |
| Output price / 1M | $89.83 | $82.19 | B |
| Context window | 2,000,000 | 2,000,000 | Tie |
| Max output | 128,000 | 8,192 | A |
| Average score | 86.1 | 86.6 | B |
| Arena Elo | 1482.0 | 1468.1 | A |
| Open weights | No | No | Tie |
Benchmark comparison
GPT-5.1 Turbo wins 6, o4 Turbo wins 5, and 1 benchmarks are tied. The table shows the modelled score for each model and the gap.
| Benchmark | GPT-5.1 Turbo | o4 Turbo | Gap | Winner |
|---|---|---|---|---|
| MMLU-Pro | 85.2 | 88.1 | 2.9 | o4 Turbo |
| GPQA Diamond | 81.3 | 84.8 | 3.5 | o4 Turbo |
| SWE-bench Verified | 74.7 | 78.4 | 3.7 | o4 Turbo |
| HumanEval | 91.5 | 91.0 | 0.5 | GPT-5.1 Turbo |
| MATH-500 | 91.4 | 91.7 | 0.3 | o4 Turbo |
| AIME 2025 | 84.7 | 85.9 | 1.2 | o4 Turbo |
| LiveCodeBench | 84.6 | 80.1 | 4.5 | GPT-5.1 Turbo |
| IFEval | 93.4 | 92.6 | 0.8 | GPT-5.1 Turbo |
| TruthfulQA | 89.2 | 88.8 | 0.4 | GPT-5.1 Turbo |
| HellaSwag | 91.3 | 91.3 | 0.0 | Tie |
| MMMU | 79.7 | 79.6 | 0.1 | GPT-5.1 Turbo |
| Arena Elo | 1482.0 | 1468.1 | 13.9 | GPT-5.1 Turbo |
Price analysis
On a blended 3:1 input-to-output basis, GPT-5.1 Turbo costs about $36.85 per million tokens and o4 Turbo costs about $35.05. o4 Turbo is roughly 5% cheaper than GPT-5.1 Turbo. 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 6, o4 Turbo wins 5, and 1 are tied. On the index average, o4 Turbo leads GPT-5.1 Turbo by 0.5 points (86.6 versus 86.1).
The price picture favours o4 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 o4 Turbo for quality-sensitive work, and check whether its price holds at your expected volume before committing.
Choose GPT-5.1 Turbo if
- You need the larger 128,000-token output limit.
Choose o4 Turbo if
- You want the higher average benchmark score in this index.
- Unit cost matters and you want the cheaper blended price.
FAQ
Is GPT-5.1 Turbo better than o4 Turbo?
On the index average, o4 Turbo leads GPT-5.1 Turbo by 0.5 points (86.6 versus 86.1). The better choice depends on price, context and your task. GPT-5.1 Turbo wins 6 benchmarks, o4 Turbo wins 5.
Which is cheaper, GPT-5.1 Turbo or o4 Turbo?
o4 Turbo is cheaper on a blended 3:1 basis at about $35.05 per million tokens, versus $36.85 for GPT-5.1 Turbo.
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; o4 Turbo is proprietary.
Which should I choose for production?
If you need a single default, start with o4 Turbo for quality-sensitive work, and check whether its price holds at your expected volume before committing.