Claude Sonnet 5.5 vs Grok 4 Fast
Claude Sonnet 5.5 leads the LLM Stats Score 58.0 to 31.7. Grok 4 Fast is 14.5x cheaper per token.
Anthropic · xAI · Updated for 2026
Which is better?
Claude Sonnet 5.5 leads the overall LLM Stats Score 58.0 to 31.7, ranking #3 overall.
On price, Grok 4 Fast is roughly 14.5x 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.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose Claude Sonnet 5.5
- overall performance matters — it scores 58.0 and ranks #3 on LLM Stats
- your work emphasizes reasoning and coding — it leads those capability indexes
- you want the most recent training data — it shipped Sep 2026
Choose Grok 4 Fast
- cost matters — it's about 14.5x cheaper per token
- you process long inputs — it offers a 2,000,000 token context window
At a glance
The differences that matter most.
Capability indexes
Additional strengths measured across groups of related public benchmarks
Individual benchmarks
47 reported for Claude Sonnet 5.5 · 7 for Grok 4 Fast
Claude Sonnet 5.5 and Grok 4 Fastdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.
Human preference
Blind head-to-head votes and playground preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, Claude Sonnet 5.5 ($2.00/1M tokens) is 10.0x more expensive than Grok 4 Fast ($0.20/1M tokens).
For output processing, Claude Sonnet 5.5 ($10.00/1M tokens) is 20.0x more expensive than Grok 4 Fast ($0.50/1M tokens).
In conclusion, Claude Sonnet 5.5 is more expensive than Grok 4 Fast.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok 4 Fast accepts 2,000,000 input tokens compared to Claude Sonnet 5.5's 1,000,000 tokens. Claude Sonnet 5.5 can generate longer responses up to 128,000 tokens, while Grok 4 Fast is limited to 30,000 tokens.
Input capabilities
Documented input modalities across available providers
Both Claude Sonnet 5.5 and Grok 4 Fast support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
Claude Sonnet 5.5
Grok 4 Fast
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
Claude Sonnet 5.5 was released on 2026-09-28, while Grok 4 Fast was released on 2025-08-28.
Claude Sonnet 5.5 is 13 months newer than Grok 4 Fast.
Sep 28, 2026
3 days ago
1.1yr newerAug 28, 2025
1.1 years ago
Knowledge Cutoff
When training data ends
Claude Sonnet 5.5 has a documented knowledge cutoff of 2026-06-01, while Grok 4 Fast's cutoff date is not specified.
We can confirm Claude Sonnet 5.5's training data extends to 2026-06-01, but cannot make a direct comparison without Grok 4 Fast's cutoff date.
Jun 2026
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Provider Availability
Claude Sonnet 5.5 is available from Anthropic. Grok 4 Fast is available from xAI.
Claude Sonnet 5.5
Grok 4 Fast
Outputs Comparison
Judge for yourself.
Run your own prompts against Claude Sonnet 5.5 and Grok 4 Fast side-by-side, then vote on the output you prefer.
FAQ
Common questions about Claude Sonnet 5.5 vs Grok 4 Fast.