Model comparison
GPT-5.5 vs Grok 4 Fast
GPT-5.5 is the stronger model overall, scoring 63.4 to 39.4 on the Noometry Index.
Last verified . 28 shared benchmarks.
Summary
- They share 28 benchmarks with published results for both. GPT-5.5 scores higher in 8 categories and Grok 4 Fast in 1 category; 9 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where GPT-5.5 leads 72.8 to 22.2.
- The biggest single-benchmark swing is ARC-AGI-2: 85% for GPT-5.5 and 5.3% for Grok 4 Fast.
Side by side
| GPT-5.5 | Grok 4 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 63.4 | 39.4 |
| Released | 2026-04-23 | 2025-09-19 |
| Weights | Proprietary | Proprietary |
| Context window | 1.05M | — |
| Max output | 128K | — |
| Input $ / M tokens | $5 | — |
| Output $ / M tokens | $30 | — |
| Results tracked | 71 | 30 |
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Category by category
Coding GPT-5.5 leads
GPT-5.5: 58.2 (#17), Grok 4 Fast: 32.5 (#271)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena WebDev | 1513 | 1159 |
| WeirdML | 84.9% | 42.9% |
| LMArena Coding | 1494 | 1429 |
| SWE-bench Verified | 80.6% | — |
| DeepSWE | 67% | — |
| FrontierCode | 43% | — |
| SciCode | 56.1% | — |
| GSO | 40.2% | — |
| MirrorCode | 10% | — |
| ALE-Bench | 1,943 | — |
Agentic & Tool Use GPT-5.5 leads
GPT-5.5: 50.7 (#6), Grok 4 Fast: 29.5 (#86)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| τ²-bench Banking | 44.6% | 15.7% |
| LMArena Search | 1242 | 1171 |
| Terminal-Bench | 84.7% | — |
| APEX-Agents | 55.1% | — |
| OSWorld 2.0 | 13% | — |
| Remote Labor Index | 6.3% | — |
| Cybench | — | 30% |
| DeepResearch Bench | 54% | — |
| PostTrainBench | 27.2% | — |
| ExploitBench | 47.4% | — |
| GBAEval | 53.2% | — |
| GDP.pdf | 26% | — |
| Vending-Bench 2 | 7,524 | — |
Reasoning GPT-5.5 leads
GPT-5.5: 72.8 (#11), Grok 4 Fast: 22.2 (#201)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| ARC-AGI-2 | 85% | 5.3% |
| Kagi LLM Benchmark | 88.8% | 66.1% |
| ARC-AGI-1 | 95% | 48.5% |
| LMArena Hard Prompts | 1489 | 1412 |
| DTBench | 96% | 82.7% |
| Epoch Capabilities Index | 159.1 | 144.2 |
| ForecastBench | 60.6 | 60.5 |
| SimpleBench | 69% | — |
| NYT Connections (extended) | 96.2% | — |
| CritPt | 27.1% | — |
| Chess Puzzles | 54% | — |
| EBR-Bench | 34.3% | — |
| Mystery Game Puzzles | 56% | — |
| LMCA | 54.3% | — |
| Surface Evolver Bench | 88.1% | — |
| Bench to the Future 3 | 0.14 | — |
Math GPT-5.5 leads
GPT-5.5: 81.7 (#11), Grok 4 Fast: 38.9 (#123)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Math | 1486 | 1419 |
| FrontierMath (Tiers 1-3) | 85.3% | — |
| FrontierMath Tier 4 | 72.5% | — |
| MathArena Final-Answer Competitions | 94.3% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 50% | — |
| FrontierMath (Feb 2025 set) | 51.7% | — |
| FrontierMath Erdős | 0% | — |
| FrontierMath Tier 4 (v1) | 35.4% | — |
Knowledge GPT-5.5 leads
GPT-5.5: 64.4 (#17), Grok 4 Fast: 32.0 (#214)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| Vectara Hallucination Rate | 9.3% | 19.7% |
| LMArena Expert | 1508 | 1411 |
| GPQA Diamond | 94% | — |
| SimpleQA Verified | 63% | — |
Multimodal Not comparable
GPT-5.5: 46.9 (#12), Grok 4 Fast: —
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Vision | 1297 | — |
| Blueprint-Bench 2 | 36.2% | — |
| Furniture Assembly | 44.2% | — |
| LMArena Document | 1486 | — |
Multilingual GPT-5.5 leads
GPT-5.5: 56.4 (#20), Grok 4 Fast: 51.3 (#111)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Non-English | 1467 | 1396 |
| LMArena Chinese | 1533 | 1457 |
| LMArena French | 1486 | 1431 |
| LMArena German | 1480 | 1383 |
| LMArena Japanese | 1498 | 1352 |
| LMArena Korean | 1460 | 1357 |
| LMArena Russian | 1473 | 1389 |
| LMArena Spanish | 1468 | 1415 |
Instruction Following GPT-5.5 leads
GPT-5.5: 77.5 (#18), Grok 4 Fast: 73.2 (#121)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Instruction Following | 1479 | 1387 |
Long Context Grok 4 Fast leads
GPT-5.5: 48.3 (#12), Grok 4 Fast: 63.2 (#3)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Longer Query | 1484 | 1415 |
| Fiction.LiveBench | — | 94.4% |
| CL-bench Life | 22.2% | — |
Writing & Preference GPT-5.5 leads
GPT-5.5: 72.7 (#13), Grok 4 Fast: 60.0 (#102)
| Benchmark | GPT-5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Text | 1472 | 1407 |
| LMArena Creative Writing | 1455 | 1387 |
| LMArena Multi-Turn | 1476 | 1414 |
| EQ-Bench Creative Writing | 1844 | — |
| EQ-Bench 4 | 1315 | — |
Frequently asked questions
Is GPT-5.5 better than Grok 4 Fast?
GPT-5.5 is the stronger model overall, scoring 63.4 to 39.4 on the Noometry Index.
Is GPT-5.5 or Grok 4 Fast better for coding?
GPT-5.5 scores higher on coding benchmarks: 58.2 versus 32.5 in the Noometry coding category.
How many benchmarks do GPT-5.5 and Grok 4 Fast share?
28 benchmarks have published results for both models. GPT-5.5 has 71 scored results on Noometry and Grok 4 Fast has 30.