Model comparison
GPT-5.1 vs Grok 4.1 Fast
GPT-5.1 is the stronger model overall, scoring 49.0 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 12× less per token, which makes it the better buy when GPT-5.1's lead doesn't matter for your workload.
Last verified . 26 shared benchmarks.
Summary
- They share 26 benchmarks with published results for both. GPT-5.1 scores higher in 8 categories and Grok 4.1 Fast in 2 categories; 10 gaps are clear of the uncertainty.
- The widest gap is in math, where GPT-5.1 leads 52.2 to 31.9.
- The biggest single-benchmark swing is Vectara Hallucination Rate: 10.9% for GPT-5.1 and 17.8% for Grok 4.1 Fast.
- Grok 4.1 Fast is cheaper at $0.20 / $0.50 per million input/output tokens, against $1.25 / $10 for GPT-5.1.
- GPT-5.1 accepts more context: 400K tokens versus 128K.
Side by side
| GPT-5.1 | Grok 4.1 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 49.0 | 41.4 |
| Released | 2025-11-13 | 2025-06-27 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 128K |
| Max output | 128K | 30K |
| Input $ / M tokens | $1.25 | $0.20 |
| Output $ / M tokens | $10 | $0.50 |
| Results tracked | 63 | 32 |
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Category by category
Coding GPT-5.1 leads
GPT-5.1: 46.4 (#66), Grok 4.1 Fast: 34.1 (#245)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena WebDev | 1395 | 1242 |
| LMArena Coding | 1454 | 1411 |
| ALE-Bench | 1,192 | 394.93 |
| SWE-bench Verified | 68% | — |
| SWE-bench Verified (bash only) | 66% | — |
| SciCode | 43.3% | — |
| GSO | 13.7% | — |
| WeirdML | 60.8% | — |
| LiveBench Coding | 72.5% | — |
Agentic & Tool Use Grok 4.1 Fast leads
GPT-5.1: 32.7 (#60), Grok 4.1 Fast: 36.3 (#39)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Search | 1199 | 1171 |
| Vending-Bench 2 | 1,473 | 1,107 |
| Terminal-Bench | 47.6% | — |
| Berkeley Function Calling Leaderboard | — | 69.6% |
| τ²-bench Banking | — | 13.1% |
| DeepResearch Bench | 42.8% | — |
Reasoning Grok 4.1 Fast leads
GPT-5.1: 39.8 (#58), Grok 4.1 Fast: 43.4 (#49)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| SimpleBench | 53.2% | 56% |
| LMArena Hard Prompts | 1457 | 1407 |
| DTBench | 90.1% | 87.7% |
| ForecastBench | 58.1 | 61 |
| ARC-AGI-2 | 17.6% | — |
| NYT Connections (extended) | — | 87.4% |
| ARC-AGI-1 | 72.8% | — |
| CritPt | 4.9% | — |
| Chess Puzzles | 32% | — |
| EnigmaEval | 11.2% | — |
| LiveBench Reasoning | 95.8% | — |
| Mystery Game Puzzles | 19% | — |
| LiveBench Data Analysis | 72.1% | — |
| LMCA | 43.9% | — |
| Epoch Capabilities Index | 149.64 | — |
| LiveBench | 78.8% | — |
Math GPT-5.1 leads
GPT-5.1: 52.2 (#51), Grok 4.1 Fast: 31.9 (#221)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Math | 1447 | 1408 |
| MathArena Final-Answer Competitions | — | 60.9% |
| OTIS Mock AIME 2024-2025 | 88.6% | — |
| ProofBench | — | 4% |
| Omni-MATH | 46.4% | — |
| LiveBench Math | 94.5% | — |
| FrontierMath (Feb 2025 set) | 31% | — |
| FrontierMath Tier 4 (v1) | 12.5% | — |
Knowledge GPT-5.1 leads
GPT-5.1: 50.6 (#71), Grok 4.1 Fast: 33.1 (#207)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| Vectara Hallucination Rate | 10.9% | 17.8% |
| LMArena Expert | 1470 | 1399 |
| GPQA Diamond | 87.6% | — |
| Humanity's Last Exam | 23.7% | — |
| SimpleQA Verified | 48% | — |
| MMLU-Pro | 57.9% | — |
| GPQA (HELM) | 44.2% | — |
Multimodal GPT-5.1 leads
GPT-5.1: 44.8 (#19), Grok 4.1 Fast: 37.0 (#76)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Vision | 1250 | 1201 |
| VPCT | 58.7% | — |
| LMArena Document | 1403 | — |
Multilingual GPT-5.1 leads
GPT-5.1: 53.8 (#56), Grok 4.1 Fast: 51.0 (#114)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Non-English | 1431 | 1391 |
| LMArena Chinese | 1495 | 1441 |
| LMArena French | 1450 | 1415 |
| LMArena German | 1438 | 1404 |
| LMArena Japanese | 1453 | 1349 |
| LMArena Korean | 1401 | 1361 |
| LMArena Russian | 1435 | 1387 |
| LMArena Spanish | 1433 | 1413 |
Instruction Following GPT-5.1 leads
GPT-5.1: 83.9 (#1), Grok 4.1 Fast: 72.7 (#133)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Instruction Following | 1443 | 1376 |
| LiveBench Instruction Following | 93.3% | — |
| IFEval | 93.5% | — |
Long Context GPT-5.1 leads
GPT-5.1: 47.6 (#14), Grok 4.1 Fast: 42.4 (#126)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Longer Query | 1447 | 1390 |
| CL-bench | 23.7% | — |
| CL-bench Life | 17.3% | — |
Writing & Preference GPT-5.1 leads
GPT-5.1: 64.5 (#55), Grok 4.1 Fast: 57.2 (#131)
| Benchmark | GPT-5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Text | 1443 | 1408 |
| LMArena Creative Writing | 1427 | 1394 |
| LMArena Multi-Turn | 1450 | 1389 |
| EQ-Bench Creative Writing | — | 1327 |
| WildBench | 86.3% | — |
| LiveBench Language | 80.2% | — |
Frequently asked questions
Is GPT-5.1 better than Grok 4.1 Fast?
GPT-5.1 is the stronger model overall, scoring 49.0 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 12× less per token, which makes it the better buy when GPT-5.1's lead doesn't matter for your workload.
Which is cheaper, GPT-5.1 or Grok 4.1 Fast?
Grok 4.1 Fast is cheaper. It lists at $0.20 per million input tokens and $0.50 per million output tokens; GPT-5.1 lists at $1.25 and $10.
Is GPT-5.1 or Grok 4.1 Fast better for coding?
GPT-5.1 scores higher on coding benchmarks: 46.4 versus 34.1 in the Noometry coding category.
Which has the bigger context window?
GPT-5.1 does, with 400K tokens against 128K.
How many benchmarks do GPT-5.1 and Grok 4.1 Fast share?
26 benchmarks have published results for both models. GPT-5.1 has 63 scored results on Noometry and Grok 4.1 Fast has 32.