# Claude Opus 5.5 vs Grok 4 Fast

> Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 39.4 on the Noometry Index.

- Canonical page: https://noometry.com/compare/claude-opus-5-5-vs-grok-4-fast
- Last updated: 2026-10-12
- Shared benchmarks: 19

## Summary

- They share 19 benchmarks with published results for both. Claude Opus 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 Claude Opus 5.5 leads 80.2 to 22.2.
- The biggest single-benchmark swing is ARC-AGI-2: 93.3% for Claude Opus 5.5 and 5.3% for Grok 4 Fast.

## Snapshot

| | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| Provider | Anthropic | xAI |
| Noometry Index | 68.6 | 39.4 |
| Rank | 3 | 167 |
| Context | 1M | — |
| Input $/M | $4 | — |
| Output $/M | $20 | — |
| Weights | Proprietary | Proprietary |

## Coding

- Claude Opus 5.5: 71.9 (#3)
- Grok 4 Fast: 32.5 (#271)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena WebDev | 1813 | 1159 |
| LMArena Coding | 1547 | 1429 |
| FrontierCode | 54.6% | — |
| CursorBench | 57.8% | — |
| FrontierSWE | 62.3% | — |
| SciCode | 66.9% | — |
| WeirdML | — | 42.9% |
| MirrorCode | 77.4% | — |
| ALE-Bench | 2,147 | — |

## Agentic & Tool Use

- Claude Opus 5.5: 45.3 (#15)
- Grok 4 Fast: 29.5 (#86)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| APEX-Agents | 73.5% | — |
| τ²-bench Banking | — | 15.7% |
| Cybench | — | 30% |
| GDP.pdf | 30.6% | — |
| LMArena Search | — | 1171 |
| Vending-Bench 2 | 9,235 | — |

## Reasoning

- Claude Opus 5.5: 80.2 (#3)
- Grok 4 Fast: 22.2 (#201)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| ARC-AGI-2 | 93.3% | 5.3% |
| ARC-AGI-1 | 98.5% | 48.5% |
| LMArena Hard Prompts | 1535 | 1412 |
| DTBench | 98.9% | 82.7% |
| Epoch Capabilities Index | 167.33 | 144.2 |
| Kagi LLM Benchmark | — | 66.1% |
| NYT Connections (extended) | 88.5% | — |
| CritPt | 31.7% | — |
| EBR-Bench | 71.4% | — |
| Mystery Game Puzzles | 71% | — |
| LMCA | 68.2% | — |
| ForecastBench | — | 60.5 |

## Math

- Claude Opus 5.5: 91.8 (#3)
- Grok 4 Fast: 38.9 (#123)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Math | 1506 | 1419 |
| FrontierMath (Tiers 1-3) | 91.2% | — |
| FrontierMath Tier 4 | 95% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| ProofBench | 100% | — |
| FrontierMath Erdős | 2.9% | — |

## Knowledge

- Claude Opus 5.5: 66.4 (#10)
- Grok 4 Fast: 32.0 (#214)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Expert | 1547 | 1411 |
| GPQA Diamond | 90.6% | — |
| SimpleQA Verified | 72.2% | — |
| Vectara Hallucination Rate | — | 19.7% |

## Multimodal

- Claude Opus 5.5: 57.8 (#1)
- Grok 4 Fast: —

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Vision | 1321 | — |
| Blueprint-Bench 2 | 51.2% | — |
| Furniture Assembly | 83.3% | — |

## Multilingual

- Claude Opus 5.5: 59.1 (#2)
- Grok 4 Fast: 51.3 (#111)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Non-English | 1507 | 1396 |
| LMArena Chinese | 1588 | 1457 |
| LMArena French | 1514 | 1431 |
| LMArena Russian | 1520 | 1389 |
| LMArena Spanish | 1507 | 1415 |
| LMArena German | — | 1383 |
| LMArena Japanese | — | 1352 |
| LMArena Korean | — | 1357 |

## Instruction Following

- Claude Opus 5.5: 80.0 (#3)
- Grok 4 Fast: 73.2 (#121)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Instruction Following | 1537 | 1387 |

## Long Context

- Claude Opus 5.5: 47.1 (#19)
- Grok 4 Fast: 63.2 (#3)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Longer Query | 1532 | 1415 |
| Fiction.LiveBench | — | 94.4% |

## Writing & Preference

- Claude Opus 5.5: 78.2 (#3)
- Grok 4 Fast: 60.0 (#102)

| Benchmark | Claude Opus 5.5 | Grok 4 Fast |
|---|---|---|
| LMArena Text | 1515 | 1407 |
| LMArena Creative Writing | 1533 | 1387 |
| LMArena Multi-Turn | 1499 | 1414 |
| EQ-Bench Creative Writing | 2050 | — |

## FAQ

### Is Claude Opus 5.5 better than Grok 4 Fast?

Claude Opus 5.5 is the stronger model overall, scoring 68.6 to 39.4 on the Noometry Index.

### Is Claude Opus 5.5 or Grok 4 Fast better for coding?

Claude Opus 5.5 scores higher on coding benchmarks: 71.9 versus 32.5 in the Noometry coding category.

### How many benchmarks do Claude Opus 5.5 and Grok 4 Fast share?

19 benchmarks have published results for both models. Claude Opus 5.5 has 44 scored results on Noometry and Grok 4 Fast has 30.