Noometry

Model comparison

GPT-5.5 Instant vs Grok 4 Fast

GPT-5.5 Instant is the stronger model overall, scoring 42.7 to 39.4 on the Noometry Index.

Last verified . 18 shared benchmarks.

GPT-5.5 Instant OpenAI

42.7

Rank #110 Confirmed

Grok 4 Fast xAI

39.4

Rank #167 Confirmed

Summary

  • They share 18 benchmarks with published results for both. GPT-5.5 Instant scores higher in 6 categories and Grok 4 Fast in 2 categories; 7 gaps are clear of the uncertainty.
  • The widest gap is in long context, where Grok 4 Fast leads 63.2 to 43.4.

Side by side

GPT-5.5 InstantGrok 4 Fast
ProviderOpenAIxAI
Noometry Index42.739.4
Released2026-05-052025-09-19
WeightsProprietaryProprietary
Context window——
Max output——
Input $ / M tokens——
Output $ / M tokens——
Results tracked2730

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Category by category

Coding GPT-5.5 Instant leads

GPT-5.5 Instant: 44.3 (#74), Grok 4 Fast: 32.5 (#271)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Coding14331429
LMArena WebDev—1159
SciCode48.6%—
WeirdML—42.9%

Agentic & Tool Use Not comparable

GPT-5.5 Instant: —, Grok 4 Fast: 29.5 (#86)

BenchmarkGPT-5.5 InstantGrok 4 Fast
τ²-bench Banking—15.7%
Cybench—30%
LMArena Search—1171

Reasoning GPT-5.5 Instant leads

GPT-5.5 Instant: 24.9 (#155), Grok 4 Fast: 22.2 (#201)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Hard Prompts14261412
Epoch Capabilities Index142.52144.2
ARC-AGI-2—5.3%
Kagi LLM Benchmark—66.1%
ARC-AGI-1—48.5%
CritPt0%—
Chess Puzzles12%—
DTBench—82.7%
ForecastBench—60.5

Math Grok 4 Fast leads

GPT-5.5 Instant: 26.5 (#259), Grok 4 Fast: 38.9 (#123)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Math14201419
FrontierMath (Tiers 1-3)26.3%—
FrontierMath Tier 42.4%—
OTIS Mock AIME 2024-202568.1%—

Knowledge GPT-5.5 Instant leads

GPT-5.5 Instant: 48.9 (#74), Grok 4 Fast: 32.0 (#214)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Expert14091411
GPQA Diamond82.5%—
Vectara Hallucination Rate—19.7%

Multimodal Not comparable

GPT-5.5 Instant: 40.0 (#52), Grok 4 Fast: —

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Vision1250—
LMArena Document1403—

Multilingual GPT-5.5 Instant leads

GPT-5.5 Instant: 52.8 (#80), Grok 4 Fast: 51.3 (#111)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Non-English14171396
LMArena Chinese14561457
LMArena French14281431
LMArena German14111383
LMArena Japanese14081352
LMArena Korean13921357
LMArena Russian14311389
LMArena Spanish14291415

Instruction Following Too close to call

GPT-5.5 Instant: 74.2 (#100), Grok 4 Fast: 73.2 (#121)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Instruction Following14061387

Long Context Grok 4 Fast leads

GPT-5.5 Instant: 43.4 (#96), Grok 4 Fast: 63.2 (#3)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Longer Query14221415
Fiction.LiveBench—94.4%

Writing & Preference GPT-5.5 Instant leads

GPT-5.5 Instant: 61.8 (#85), Grok 4 Fast: 60.0 (#102)

BenchmarkGPT-5.5 InstantGrok 4 Fast
LMArena Text14191407
LMArena Creative Writing14191387
LMArena Multi-Turn14331414

Frequently asked questions

Is GPT-5.5 Instant better than Grok 4 Fast?

GPT-5.5 Instant is the stronger model overall, scoring 42.7 to 39.4 on the Noometry Index.

Is GPT-5.5 Instant or Grok 4 Fast better for coding?

GPT-5.5 Instant scores higher on coding benchmarks: 44.3 versus 32.5 in the Noometry coding category.

How many benchmarks do GPT-5.5 Instant and Grok 4 Fast share?

18 benchmarks have published results for both models. GPT-5.5 Instant has 27 scored results on Noometry and Grok 4 Fast has 30.

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