Grok 4.1 Fast vs GPT-5.1 Chat
Grok 4.1 Fast comes out ahead, 71 to 38 on our weighted score, and it is the cheaper option too.
- Our pick
xAIGrok 4.1 Fast
71/100- ECI—
- Price$0.20 / $0.50
- Context2M
OpenAIGPT-5.1 Chat
38/100- ECI—
- Price$1.25 / $10.00
- Context128K
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Make it a three-way comparison.
Grok 4.1 Fast is our pick
Grok 4.1 Fast is the better all-round choice, scoring 71/100 against GPT-5.1 Chat (38). It leads on price and context window. GPT-5.1 Chat wins on inputs & features. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceGrok 4.1 FastGrok 4.1 Fast $0.275 · GPT-5.1 Chat $3.44 per 1M tokens (3:1 blend)
- Longest contextGrok 4.1 FastGrok 4.1 Fast 2,000,000 · GPT-5.1 Chat 128,000 tokens
- Widest inputsSame inputsGrok 4.1 Fast: Text, Images · GPT-5.1 Chat: Text, Images
- Self-hostingNo open weightsBoth are available only through APIs
| Measure | Weight | Grok 4.1 Fast | GPT-5.1 Chat |
|---|---|---|---|
| Price | 50% | 76 | 24 |
| Inputs & features | 30% | 60 | 70 |
| Context window | 20% | 72 | 24 |
| Overall | 100% | 71/100 | 38/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Grok 4.1 FastxAI | GPT-5.1 ChatOpenAI |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | — | — |
| ECI rank | — | — |
| Price per million tokens | ||
| Input | $0.20 (best) | $1.25 |
| Output | $0.50 (best) | $10.00 |
| Cached input | — | — |
| Blended (3:1) | $0.275 (best) | $3.44 |
| Long-context rate | Same rate | Same rate |
| Price source | Median of 2 providers | Median of 2 providers |
| Limits | ||
| Context window | 2,000,000 tokens (best) | 128,000 tokens |
| Max output | 30,000 tokens (best) | 16,384 tokens |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | Yes |
| PDFs | No | No |
| Audio | No | No |
| Video | No | No |
| Reasoning | No | Yes |
| Tool calling | Yes | Yes |
| Structured output | Yes | Yes |
| Availability | ||
| Weights | Proprietary | Proprietary |
| API model ID | — | — |
| API providers | 2 | 2 |
| Released | Nov 19, 2025 | Nov 13, 2025 |
| Knowledge cutoff | — | Sep 30, 2024 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Grok 4.1 Fast$3.00
- GPT-5.1 Chat$32.50
Which should you choose?
Which is better: Grok 4.1 Fast or GPT-5.1 Chat?
Grok 4.1 Fast is the better all-round choice, scoring 71/100 against GPT-5.1 Chat (38). It leads on price and context window. GPT-5.1 Chat wins on inputs & features. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Grok 4.1 Fast or GPT-5.1 Chat?
Grok 4.1 Fast is cheaper at $0.20 input / $0.50 output per million tokens (median across 2 API providers). GPT-5.1 Chat costs $1.25 input / $10.00 output per million tokens (median across 2 API providers). At a typical mix of three input tokens to one output token, that is $0.275 per million tokens for Grok 4.1 Fast versus $3.44 for GPT-5.1 Chat (12× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers both models yet. Grok 4.1 Fast has not been scored yet and GPT-5.1 Chat has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Grok 4.1 Fast and GPT-5.1 Chat yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.
Which has the bigger context window?
Grok 4.1 Fast has the largest context window at 2,000,000 tokens, against 128,000 for GPT-5.1 Chat. Maximum output per response: Grok 4.1 Fast up to 30,000, GPT-5.1 Chat up to 16,384 tokens.
Which can read images, PDFs, audio or video?
Grok 4.1 Fast accepts text and images; GPT-5.1 Chat accepts text and images. They handle the same number of input types.
Are any of these open source?
No. Grok 4.1 Fast and GPT-5.1 Chat are proprietary and only available through APIs and apps.
Which is newer?
Grok 4.1 Fast is the newest, released Nov 19, 2025. GPT-5.1 Chat came out Nov 13, 2025. Knowledge cutoff: GPT-5.1 Chat Sep 30, 2024.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
