Model Comparison

Grok 4 Fast vs Grok-4 Heavy

Grok-4 Heavy shows notably better performance in the majority of benchmarks.

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Performance Benchmarks

Comparative analysis across standard metrics

4 benchmarks

Grok 4 Fast outperforms in 1 benchmarks (LiveCodeBench), while Grok-4 Heavy is better at 3 benchmarks (AIME 2025, GPQA, Humanity's Last Exam).

Grok-4 Heavy shows notably better performance in the majority of benchmarks.

Mon Apr 27 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Cost data unavailable.

Lowest available price from all providers
Mon Apr 27 2026 • llm-stats.com
xAI
Grok 4 Fast
Input tokens$0.20
Output tokens$0.50
Best providerxAI
xAI
Grok-4 Heavy
Input tokens$0.00
Output tokens$0.00
Best providerUnknown Organization
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Context Window

Maximum input and output token capacity

Only Grok 4 Fast specifies input context (2,000,000 tokens). Only Grok 4 Fast specifies output context (30,000 tokens).

xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
xAI
Grok-4 Heavy
Input- tokens
Output- tokens
Mon Apr 27 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Grok 4 Fast and Grok-4 Heavy support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

Grok 4 Fast

Text
Images
Audio
Video

Grok-4 Heavy

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

Grok 4 Fast

Proprietary

Closed source

Grok-4 Heavy

Proprietary

Closed source

Release Timeline

When each model was launched

Grok 4 Fast was released on 2025-08-28, while Grok-4 Heavy's release date is not specified.

We can confirm Grok 4 Fast's release timeline, but cannot make a direct age comparison without Grok-4 Heavy's release date.

Grok 4 Fast

Aug 28, 2025

8 months ago

Grok-4 Heavy

—

Knowledge Cutoff

When training data ends

Grok-4 Heavy has a documented knowledge cutoff of 2024-12-31, while Grok 4 Fast's cutoff date is not specified.

We can confirm Grok-4 Heavy's training data extends to 2024-12-31, but cannot make a direct comparison without Grok 4 Fast's cutoff date.

Grok 4 Fast

—

Grok-4 Heavy

Dec 2024

Outputs Comparison

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Key Takeaways

xAI
Larger context window (2,000,000 tokens)
Higher LiveCodeBench score (80.0% vs 79.4%)
xAI
Higher AIME 2025 score (100.0% vs 92.0%)
Higher GPQA score (88.4% vs 85.7%)
Higher Humanity's Last Exam score (50.7% vs 20.0%)

Detailed Comparison

AI Model Comparison Table
Feature
xAI
Grok 4 Fast
xAI
Grok-4 Heavy

FAQ

Common questions about Grok 4 Fast vs Grok-4 Heavy

Grok-4 Heavy shows notably better performance in the majority of benchmarks. Grok 4 Fast is made by xAI and Grok-4 Heavy is made by xAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.
Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%. Grok-4 Heavy scores AIME 2025: 100.0%, HMMT25: 96.7%, GPQA: 88.4%, LiveCodeBench: 79.4%, USAMO25: 61.9%.
Grok 4 Fast supports 2.0M tokens and Grok-4 Heavy supports an unknown number of tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.