Model Comparison

Grok 4 Fast vs Grok 4.5Which is better in 2026?

Grok 4.5 significantly outperforms across most benchmarks. Grok 4 Fast is 10.9x cheaper per token.

Verdict: Grok 4 Fast vs Grok 4.5 — which is better?

Grok 4 Fast (by xAI) and Grok 4.5 (by xAI) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.

Grok 4 Fast outperforms in 0 benchmarks, while Grok 4.5 is better at 1 benchmark (GPQA). Grok 4.5 significantly outperforms across most benchmarks.

On price, Grok 4 Fast is roughly 10.9x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok 4 Fast also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose Grok 4 Fast if…

  • cost matters — it's about 10.9x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window

Choose Grok 4.5 if…

  • you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
  • you want the most recent training data — it shipped Jul 2026

Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

Grok 4 Fast outperforms in 0 benchmarks, while Grok 4.5 is better at 1 benchmark (GPQA).

Grok 4.5 significantly outperforms across most benchmarks.

Tue Jul 21 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Grok 4 Fast costs less

For input processing, Grok 4 Fast ($0.20/1M tokens) is 10.0x cheaper than Grok 4.5 ($2.00/1M tokens).

For output processing, Grok 4 Fast ($0.50/1M tokens) is 12.0x cheaper than Grok 4.5 ($6.00/1M tokens).

In conclusion, Grok 4.5 is more expensive than Grok 4 Fast.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Tue Jul 21 2026 • llm-stats.com
xAI
Grok 4 Fast
Input tokens$0.20
Output tokens$0.50
Best providerxAI
xAI
Grok 4.5
Input tokens$2.00
Output tokens$6.00
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok 4 Fast accepts 2,000,000 input tokens compared to Grok 4.5's 500,000 tokens. Only Grok 4 Fast specifies output context (30,000 tokens).

xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
xAI
Grok 4.5
Input500,000 tokens
Output- tokens
Tue Jul 21 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Grok 4 Fast and Grok 4.5 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 4.5

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 4.5

Proprietary

Closed source

Release Timeline

When each model was launched

Grok 4 Fast was released on 2025-08-28, while Grok 4.5 was released on 2026-07-16.

Grok 4.5 is 11 months newer than Grok 4 Fast.

Grok 4 Fast

Aug 28, 2025

10 months ago

Grok 4.5

Jul 16, 2026

5 days ago

10mo newer

Knowledge Cutoff

When training data ends

Grok 4.5 has a documented knowledge cutoff of 2026-02-01, while Grok 4 Fast's cutoff date is not specified.

We can confirm Grok 4.5's training data extends to 2026-02-01, but cannot make a direct comparison without Grok 4 Fast's cutoff date.

Grok 4 Fast

—

Grok 4.5

Feb 2026

Provider Availability

Grok 4 Fast is available from xAI. Grok 4.5 is available from xAI.

Grok 4 Fast

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M

Grok 4.5

xai logo
xAI
Input Price:Input: $2.00/1MOutput Price:Output: $6.00/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

xAI
Larger context window (2,000,000 tokens)
Less expensive input tokens
Less expensive output tokens
xAI
Higher GPQA score (93.0% vs 85.7%)

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against Grok 4 Fast and Grok 4.5 side-by-side, then vote on the output you prefer.

Grok 4 Fast
✓ Preferred
Grok 4.5
Open in Playground
AI Model Comparison Table
Feature
xAI
Grok 4 Fast
xAI
Grok 4.5

FAQ

Common questions about Grok 4 Fast vs Grok 4.5.

Which is better, Grok 4 Fast or Grok 4.5?

Grok 4.5 significantly outperforms across most benchmarks. Grok 4 Fast is made by xAI and Grok 4.5 is made by xAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does Grok 4 Fast compare to Grok 4.5 in benchmarks?

Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%. Grok 4.5 scores GPQA: 93.0%, Terminal-Bench 2.1: 83.3%, Artificial Analysis Coding Agent Index v1.1: 76.0%, SWE-Bench Pro: 64.7%, AA-Omniscience Index: 63.0%.

Is Grok 4 Fast cheaper than Grok 4.5?

Grok 4 Fast is 10.0x cheaper for input tokens. Grok 4 Fast costs $0.20/M input and $0.50/M output via xai. Grok 4.5 costs $2.00/M input and $6.00/M output via xai.

What are the context window sizes for Grok 4 Fast and Grok 4.5?

Grok 4 Fast supports 2.0M tokens and Grok 4.5 supports 500K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between Grok 4 Fast and Grok 4.5?

Key differences include context window (2.0M vs 500K), input pricing ($0.20 vs $2.00/M). See the full comparison above for benchmark-by-benchmark results.

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