Model comparison
GPT-5.5 Pro vs Grok 4 Fast
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 39.4 on the Noometry Index.
Last verified . 4 shared benchmarks.
Summary
- They share 4 benchmarks with published results for both. GPT-5.5 Pro scores higher in 3 categories and Grok 4 Fast in 0 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where GPT-5.5 Pro leads 73.3 to 22.2.
- The biggest single-benchmark swing is ARC-AGI-2: 84.6% for GPT-5.5 Pro and 5.3% for Grok 4 Fast.
Side by side
| GPT-5.5 Pro | Grok 4 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 64.3 | 39.4 |
| Released | 2026-04-23 | 2025-09-19 |
| Weights | Proprietary | Proprietary |
| Context window | 1.05M | — |
| Max output | 128K | — |
| Input $ / M tokens | $30 | — |
| Output $ / M tokens | $180 | — |
| Results tracked | 14 | 30 |
Sponsored placements are available on pages like this one. Advertise on Noometry
Category by category
Coding Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 32.5 (#271)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| LMArena WebDev | — | 1159 |
| WeirdML | — | 42.9% |
| LMArena Coding | — | 1429 |
Agentic & Tool Use Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 29.5 (#86)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| τ²-bench Banking | — | 15.7% |
| Cybench | — | 30% |
| LMArena Search | — | 1171 |
Reasoning GPT-5.5 Pro leads
GPT-5.5 Pro: 73.3 (#10), Grok 4 Fast: 22.2 (#201)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| ARC-AGI-2 | 84.6% | 5.3% |
| ARC-AGI-1 | 96.5% | 48.5% |
| DTBench | 96% | 82.7% |
| Epoch Capabilities Index | 162.07 | 144.2 |
| SimpleBench | 76.9% | — |
| Kagi LLM Benchmark | — | 66.1% |
| CritPt | 30.6% | — |
| Chess Puzzles | 64% | — |
| LMArena Hard Prompts | — | 1412 |
| LMCA | 53.9% | — |
| ForecastBench | — | 60.5 |
Math GPT-5.5 Pro leads
GPT-5.5 Pro: 84.0 (#10), Grok 4 Fast: 38.9 (#123)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| FrontierMath (Tiers 1-3) | 87.7% | — |
| FrontierMath Tier 4 | 78% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| LMArena Math | — | 1419 |
| FrontierMath (Feb 2025 set) | 52.4% | — |
| FrontierMath Tier 4 (v1) | 39.6% | — |
Knowledge GPT-5.5 Pro leads
GPT-5.5 Pro: 64.1 (#19), Grok 4 Fast: 32.0 (#214)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| GPQA Diamond | 93.9% | — |
| Vectara Hallucination Rate | — | 19.7% |
| LMArena Expert | — | 1411 |
Multilingual Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 51.3 (#111)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| LMArena Non-English | — | 1396 |
| LMArena Chinese | — | 1457 |
| LMArena French | — | 1431 |
| LMArena German | — | 1383 |
| LMArena Japanese | — | 1352 |
| LMArena Korean | — | 1357 |
| LMArena Russian | — | 1389 |
| LMArena Spanish | — | 1415 |
Instruction Following Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 73.2 (#121)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| LMArena Instruction Following | — | 1387 |
Long Context Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 63.2 (#3)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| Fiction.LiveBench | — | 94.4% |
| LMArena Longer Query | — | 1415 |
Writing & Preference Not comparable
GPT-5.5 Pro: —, Grok 4 Fast: 60.0 (#102)
| Benchmark | GPT-5.5 Pro | Grok 4 Fast |
|---|---|---|
| LMArena Text | — | 1407 |
| LMArena Creative Writing | — | 1387 |
| LMArena Multi-Turn | — | 1414 |
Frequently asked questions
Is GPT-5.5 Pro better than Grok 4 Fast?
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 39.4 on the Noometry Index.
How many benchmarks do GPT-5.5 Pro and Grok 4 Fast share?
4 benchmarks have published results for both models. GPT-5.5 Pro has 14 scored results on Noometry and Grok 4 Fast has 30.