> Grok 4 Fast is a closed AI model from xAI, released 19 Sep 2025. Index score 143 (GPT-4 = 100), rank 79 of 229 ranked models.

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# Grok 4 Fast

xAI

Released 19 Sep 2025

Closed

Small / fast

Date verified

[Compare](https://themodelindex.org/compare/grok-4-fast-vs-deepseek-v3-2-exp/) [Announcement](https://x.ai/news/grok-4-fast)

143132–155

Index score

#79 of 229 models

1/ 8

Core tests taken

1 of 6 areas · plus 4 anchor tests

−11

Versus the frontier at release

best then: GPT-5

Replaced by [Grok 4.1 Fast](https://themodelindex.org/models/grok-4-1-fast/)

–

Price per million tokens

no public API price found

–

Context window

tokens it reads at once

## Where it sits · on the frontier

_Chart: Model Index score of every scored model since late 2022, with the best closed and best open model over time_

o3 reached this score 5 months earlier.

## Test results · by area · tick = best by any model

Show 3 anchor tests

Reasoning & knowledge

no evidence yet

GPQA Diamond

no result

Humanity's Last Exam

no result

Maths

no evidence yet

FrontierMath T1-3

no result

Coding

evidence

SWE-bench Verified

no result

Terminal-Bench

no result

Agents

evidence

APEX-Agents

no result

Novel problems

evidence

ARC-AGI-2

5%

Long tasks

no evidence yet

METR time horizon

no result

Independent results from the Epoch AI benchmarking hub, best reasoning setting. The core tests are shown here; anchor tests also inform the score and can be shown above.

## What others say · rank on each leaderboard

The Model Index

independent tests, our method

#79

of 219 · 143

LMArena · Maths

maths questions in chat

#104

of 373 · 1425

LMArena · Text

overall chat quality, judged by people

#112

of 388 · 1419

LMArena · Creative writing

creative writing

#119

of 386 · 1384

LMArena · Coding

coding questions in chat

#125

of 383 · 1458

Epoch Capabilities Index

overall capability from many benchmarks

#83

of 239 · 144.2

LMArena · WebDev

building web apps and front ends

#122

of 123 · 1159

Further left is better. Leaderboards measure different things: LMArena is people voting blind between two answers, the others are test scores. Click any row for the source.

## Best at · top three among current models

Replaced by Grok 4.1 Fast; it no longer leads any category among current models.

Where this model places in the top three of today's models, on category leaderboards and on our core tests.

## Where to use it · prices checked 1 Oct 2026

#### From the lab

Grok

app · subscription

↗

xAI API

API

↗

Provider prices come from OpenRouter's live listing; going direct to a provider can differ. Subscriptions are the lab's own apps.

## Facts and sources

Released

19 Sep 2025

Announcement

[x.ai ↗](https://x.ai/news/grok-4-fast)

Release entry

Grok 4 Fast

Scored as

Grok 4 Fast

Artificial Analysis index

–

Output speed

–

Hugging Face

closed weights

## xAI releases · around this one

Grok 2.5

Open

23 AUG 2025

Grok Code Fast 1

Closed

28 AUG 2025

Grok 4 Fast

Closed

19 SEP 2025

index 143

Grok 4.1

Closed

17 NOV 2025

Grok 4.1 Fast

Closed

19 NOV 2025

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Source: https://themodelindex.org/models/grok-4-fast/ · The Model Index · data as of 2026-10-01