Model Comparison

Claude Sonnet 4.5 vs Grok 4 Fast

Grok 4 Fast significantly outperforms across most benchmarks. Grok 4 Fast is 21.8x cheaper per token.

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Performance Benchmarks

Comparative analysis across standard metrics

2 benchmarks

Claude Sonnet 4.5 outperforms in 0 benchmarks, while Grok 4 Fast is better at 2 benchmarks (AIME 2025, GPQA).

Grok 4 Fast significantly outperforms across most benchmarks.

Sat May 02 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Grok 4 Fast costs less

For input processing, Claude Sonnet 4.5 ($3.00/1M tokens) is 15.0x more expensive than Grok 4 Fast ($0.20/1M tokens).

For output processing, Claude Sonnet 4.5 ($15.00/1M tokens) is 30.0x more expensive than Grok 4 Fast ($0.50/1M tokens).

In conclusion, Claude Sonnet 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
Sat May 02 2026 • llm-stats.com
Anthropic
Claude Sonnet 4.5
Input tokens$3.00
Output tokens$15.00
Best providerAnthropic
xAI
Grok 4 Fast
Input tokens$0.20
Output tokens$0.50
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 Claude Sonnet 4.5's 200,000 tokens. Claude Sonnet 4.5 can generate longer responses up to 64,000 tokens, while Grok 4 Fast is limited to 30,000 tokens.

Anthropic
Claude Sonnet 4.5
Input200,000 tokens
Output64,000 tokens
xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
Sat May 02 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Claude Sonnet 4.5 and Grok 4 Fast support multimodal inputs.

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

Claude Sonnet 4.5

Text
Images
Audio
Video

Grok 4 Fast

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.

Claude Sonnet 4.5

Proprietary

Closed source

Grok 4 Fast

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Sonnet 4.5 was released on 2025-09-29, while Grok 4 Fast was released on 2025-08-28.

Claude Sonnet 4.5 is 1 month newer than Grok 4 Fast.

Claude Sonnet 4.5

Sep 29, 2025

7 months ago

1mo newer
Grok 4 Fast

Aug 28, 2025

8 months ago

Knowledge Cutoff

When training data ends

Claude Sonnet 4.5 has a documented knowledge cutoff of 2025-01-31, while Grok 4 Fast's cutoff date is not specified.

We can confirm Claude Sonnet 4.5's training data extends to 2025-01-31, but cannot make a direct comparison without Grok 4 Fast's cutoff date.

Claude Sonnet 4.5

Jan 2025

Grok 4 Fast

—

Provider Availability

Claude Sonnet 4.5 is available from Anthropic. Grok 4 Fast is available from xAI.

Claude Sonnet 4.5

anthropic logo
Anthropic
Input Price:Input: $3.00/1MOutput Price:Output: $15.00/1M

Grok 4 Fast

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

Anthropic

No standout differentiators in the data we have for this pair.

xAI
Larger context window (2,000,000 tokens)
Less expensive input tokens
Less expensive output tokens
Higher AIME 2025 score (92.0% vs 87.0%)
Higher GPQA score (85.7% vs 83.4%)

Detailed Comparison

AI Model Comparison Table
Feature
Anthropic
Claude Sonnet 4.5
xAI
Grok 4 Fast

FAQ

Common questions about Claude Sonnet 4.5 vs Grok 4 Fast.

Which is better, Claude Sonnet 4.5 or Grok 4 Fast?

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

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

Claude Sonnet 4.5 scores MMMLU: 89.1%, AIME 2025: 87.0%, TAU-bench Retail: 86.2%, GPQA: 83.4%, MMMUval: 77.8%. Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%.

Is Claude Sonnet 4.5 cheaper than Grok 4 Fast?

Grok 4 Fast is 15.0x cheaper for input tokens. Claude Sonnet 4.5 costs $3.00/M input and $15.00/M output via anthropic. Grok 4 Fast costs $0.20/M input and $0.50/M output via xai.

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

Claude Sonnet 4.5 supports 200K tokens and Grok 4 Fast supports 2.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

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

Key differences include context window (200K vs 2.0M), input pricing ($3.00 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Sonnet 4.5 and Grok 4 Fast?

Claude Sonnet 4.5 is developed by Anthropic and Grok 4 Fast is developed by xAI.