Noometry

Model comparison

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.

Last verified . 19 shared benchmarks.

Claude Opus 5.5 Anthropic

68.6

Rank #3 Confirmed

Grok 4 Fast xAI

39.4

Rank #167 Confirmed

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.

Side by side

Claude Opus 5.5Grok 4 Fast
ProviderAnthropicxAI
Noometry Index68.639.4
Released2026-09-222025-09-19
WeightsProprietaryProprietary
Context window1M—
Max output128K—
Input $ / M tokens$4—
Output $ / M tokens$20—
Results tracked4430

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Category by category

Coding Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena WebDev18131159
LMArena Coding15471429
FrontierCode54.6%—
CursorBench57.8%—
FrontierSWE62.3%—
SciCode66.9%—
WeirdML—42.9%
MirrorCode77.4%—
ALE-Bench2,147—

Agentic & Tool Use Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
APEX-Agents73.5%—
τ²-bench Banking—15.7%
Cybench—30%
GDP.pdf30.6%—
LMArena Search—1171
Vending-Bench 29,235—

Reasoning Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
ARC-AGI-293.3%5.3%
ARC-AGI-198.5%48.5%
LMArena Hard Prompts15351412
DTBench98.9%82.7%
Epoch Capabilities Index167.33144.2
Kagi LLM Benchmark—66.1%
NYT Connections (extended)88.5%—
CritPt31.7%—
EBR-Bench71.4%—
Mystery Game Puzzles71%—
LMCA68.2%—
ForecastBench—60.5

Math Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Math15061419
FrontierMath (Tiers 1-3)91.2%—
FrontierMath Tier 495%—
OTIS Mock AIME 2024-2025100%—
ProofBench100%—
FrontierMath Erdős2.9%—

Knowledge Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Expert15471411
GPQA Diamond90.6%—
SimpleQA Verified72.2%—
Vectara Hallucination Rate—19.7%

Multimodal Not comparable

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Vision1321—
Blueprint-Bench 251.2%—
Furniture Assembly83.3%—

Multilingual Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Non-English15071396
LMArena Chinese15881457
LMArena French15141431
LMArena Russian15201389
LMArena Spanish15071415
LMArena German—1383
LMArena Japanese—1352
LMArena Korean—1357

Instruction Following Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Instruction Following15371387

Long Context Grok 4 Fast leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Longer Query15321415
Fiction.LiveBench—94.4%

Writing & Preference Claude Opus 5.5 leads

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

BenchmarkClaude Opus 5.5Grok 4 Fast
LMArena Text15151407
LMArena Creative Writing15331387
LMArena Multi-Turn14991414
EQ-Bench Creative Writing2050—

Frequently asked questions

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.

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