What is the difference between Claude Sonnet 4 and Grok 4 Fast (free)?

Claude Sonnet 4 is developed by Anthropic while Grok 4 Fast (free) is developed by xAI. Claude Sonnet 4 has a 200K token context window vs Grok 4 Fast (free)'s 2.0M. You can compare their actual outputs across 35 challenges on Rival to see how they differ in practice.

Which is better, Claude Sonnet 4 or Grok 4 Fast (free)?

It depends on your use case. Claude Sonnet 4 and Grok 4 Fast (free) each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 35 challenges so you can judge which fits your needs best.

How much does Claude Sonnet 4 cost compared to Grok 4 Fast (free)?

Claude Sonnet 4 costs $3/M input tokens and Grok 4 Fast (free) costs $0/M input tokens. Grok 4 Fast (free) is $3.00/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

How can I compare Claude Sonnet 4 and Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of Claude Sonnet 4 and Grok 4 Fast (free) across shared challenges. You can vote on which model produced the better output in a blind duel. Browsing and voting are free. No account is needed to look; signing in only saves your votes and likes.

Updated Sep 2025

Claude Sonnet 4vsGrok 4 Fast (free)

Grok 4 Fast (free) is cheaper than Claude Sonnet 4 at $0/M vs $3/M input tokens.

Claude Sonnet 4 and Grok 4 Fast (free) compared across 35 shared prompts
Spec	Claude Sonnet 4	Grok 4 Fast (free)
Input price	$3/M tokens	Free
Output price	$15/M tokens	Free
Context window	200K tokens	2.0M tokens
Parameters	Not disclosed	Not disclosed
Weights	Closed	—
Free API (OpenRouter)	No	No
Released	May 2025	Sep 2025