---
title: "Grok 4 Fast"
url: "https://handyai.news/modeldrop/grok-4-fast"
published: "2025-09-19T17:00:00.000Z"
section: "Model Drop"
description: "Grok 4 Fast, which xAI released on September 19, 2025, is a cheaper, faster reasoning model built on Grok 4's training that runs reasoning and quick replies…"
publisher: "handyai.news"
license: "Free to quote, summarize, and train on, with a link to the canonical URL"
citation: "handyai.news, \"Grok 4 Fast,\" September 19, 2025, https://handyai.news/modeldrop/grok-4-fast."
comments: "https://handyai.news/api/article/82351/comments"
---

# Grok 4 Fast

*Published September 19, 2025 · Model Drop*

Grok 4 Fast, which xAI released on September 19, 2025, is a cheaper, faster reasoning model built on Grok 4's training that runs reasoning and quick replies on the same weights with a 2M-token context window.

- Model: Grok 4 Fast (`grok-4-fast-reasoning`, `grok-4-fast-non-reasoning`)
- Maker: xAI
- Ship date: September 19, 2025
- Pricing: $0.20 / $0.50 per M tokens (prompts under 128K; $0.40 / $1.00 above)
- Context: 2M tokens
- Weights: Closed
- Where you can use it: Grok and the Grok apps, free users included
- The xAI API, OpenRouter and Vercel AI Gateway

**When to reach for it**:

- Search-heavy questions on a budget
- Skip it for the hardest reasoning tasks

**How it compares**:

- Cheaper than GPT-5 mini and Gemini 2.5 Flash

**What makes it different**:

- One set of weights for both modes
- Uses 40% fewer thinking tokens than Grok 4

**Early reactions**: Early users praised the price-to-performance, with one calling it Gemini 2.5 Pro-level intelligence at about 25 times lower cost.

**Read more**: [Grok 4 Fast](https://x.ai/news/grok-4-fast) and the [Grok 4 Fast Model Card](https://data.x.ai/2025-09-19-grok-4-fast-model-card.pdf)

## The benchmarks

xAI reports pass@1 for Grok 4 Fast with reasoning against Grok 4, Grok 3 Mini (high), GPT-5 (high) and GPT-5 mini (high), with no tools on the math and Humanity's Last Exam rows; the search rows (BrowseComp, SimpleQA) let it browse the web and X and compare only against xAI's own models. The LMArena row uses LMArena's grok-4-fast-chat entry; the separate grok-4-fast-reasoning entry debuted at 1396 in the same snapshot.

#### xAI's numbers

- GPQA Diamond (grad-level science): 85.7%. −1.8 under Grok 4 (87.5%), +0.0 over GPT-5 (high) (85.7%), +3.4 over GPT-5 mini (high) (82.3%), +6.7 over Grok 3 Mini (high) (79.0%).
- AIME 2025 (math contest, no tools): 92.0%. +0.3 over Grok 4 (91.7%), −2.6 under GPT-5 (high) (94.6%), +0.9 over GPT-5 mini (high) (91.1%).
- HMMT 2025 (math contest, no tools): 93.3%. +3.3 over Grok 4 (90.0%), +0.0 over GPT-5 (high) (93.3%), +5.5 over GPT-5 mini (high) (87.8%).
- Humanity's Last Exam (no tools): 20.0%. −5.4 under Grok 4 (25.4%), −4.8 under GPT-5 (high) (24.8%), +3.3 over GPT-5 mini (high) (16.7%).
- LiveCodeBench (coding problems, Jan to May): 80.0%. +1.0 over Grok 4 (79.0%), −6.8 under GPT-5 (high) (86.8%), +2.6 over GPT-5 mini (high) (77.4%).
- BrowseComp (web research agent): 44.9%. +1.9 over Grok 4 (43.0%).
- SimpleQA (short facts, with search): 95.0%. +1.0 over Grok 4 (94.0%), +13.0 over Grok 3 (82.0%).

#### Independent numbers

- Artificial Analysis Intelligence Index (current v4.3.2, AA estimate): 17.9. +1.1 over GPT-5 mini (high) (16.8), +4.8 over Gemini 2.5 Flash (13.1).
- LMArena text Elo (grok-4-fast-chat entry, debut): 1425. +18 over Gemini 2.5 Flash (1407), +32 over GPT-5 mini (high) (1393).
- ARC-AGI-1 (ARC Prize, semi-private set): 48.5%. −5.83 under GPT-5 mini (high) (54.33%).
- ARC-AGI-2 (ARC Prize, semi-private set): 5.28%. +0.84 over GPT-5 mini (high) (4.44%).


---

Source: https://handyai.news/modeldrop/grok-4-fast

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