What is the difference between Claude Opus 5 and xAI: Grok 4 Fast (free)?

Claude Opus 5 is developed by Anthropic while xAI: Grok 4 Fast (free) is developed by xAI. Claude Opus 5 has a 1.0M token context window vs xAI: Grok 4 Fast (free)'s 2.0M. You can compare their actual outputs across 34 challenges on Rival to see how they differ in practice.

Which is better, Claude Opus 5 or xAI: Grok 4 Fast (free)?

It depends on your use case. Claude Opus 5 and xAI: Grok 4 Fast (free) each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 34 challenges so you can judge which fits your needs best.

How much does Claude Opus 5 cost compared to xAI: Grok 4 Fast (free)?

Claude Opus 5 costs $5/M input tokens and xAI: Grok 4 Fast (free) costs $0/M input tokens. xAI: Grok 4 Fast (free) is $5.00/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 Opus 5 and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of Claude Opus 5 and xAI: 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.

What is the difference between Claude Opus 5 and xAI: Grok 4 Fast (free)?

Claude Opus 5 is developed by Anthropic while xAI: Grok 4 Fast (free) is developed by xAI. Claude Opus 5 has a 1.0M token context window vs xAI: Grok 4 Fast (free)'s 2.0M. You can compare their actual outputs across 34 challenges on Rival to see how they differ in practice.

Which is better, Claude Opus 5 or xAI: Grok 4 Fast (free)?

It depends on your use case. Claude Opus 5 and xAI: Grok 4 Fast (free) each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 34 challenges so you can judge which fits your needs best.

How much does Claude Opus 5 cost compared to xAI: Grok 4 Fast (free)?

Claude Opus 5 costs $5/M input tokens and xAI: Grok 4 Fast (free) costs $0/M input tokens. xAI: Grok 4 Fast (free) is $5.00/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 Opus 5 and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of Claude Opus 5 and xAI: 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.

Claude Opus 5 vs xAI: Grok 4 Fast (free): Which Is Better?

Updated Jul 2026

Our Verdict

Claude Opus 5

xAI: Grok 4 Fast (free)Runner-up

No community votes yet. On paper, Claude Opus 5 has the edge — bigger model tier, newer.

Too close to call

API pricing

Cost per 1M tokens

Claude Opus 5

Input

$5.00

Output

$25.00

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

44%

Claude Opus 5 uses 1.7x more emoji

Claude Opus 5

xAI: Grok 4 Fast (free)

54%Vocabulary65%

21wSentence Length13w

0.40Hedging0.56

3.9Bold1.4

1.9Lists2.5

0.02Emoji0.00

0.71Headings1.58

0.05Transitions0.28

Based on 27 + 14 text responses

Research

What we learned reading every model

Claude Opus 5 and xAI: Grok 4 Fast (free) have opinions about your brand too.Ask 10 models what they tell people about you. Verbatim receipts.Run the mirror

FAQ

Common questions

Keep exploring

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xAI: Grok 4 Fast (free) vs Gemini 2.5 Pro Preview 06-05New provider

xAI: Grok 4 Fast (free) vs GPT-5New provider

Updated Jul 2026

Our Verdict

Claude Opus 5

xAI: Grok 4 Fast (free)Runner-up

No community votes yet. On paper, Claude Opus 5 has the edge — bigger model tier, newer.

Too close to call

API pricing

Cost per 1M tokens

Claude Opus 5

Input

$5.00

Output

$25.00

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

44%

Claude Opus 5 uses 1.7x more emoji

Claude Opus 5

xAI: Grok 4 Fast (free)

54%Vocabulary65%

21wSentence Length13w

0.40Hedging0.56

3.9Bold1.4

1.9Lists2.5

0.02Emoji0.00

0.71Headings1.58

0.05Transitions0.28

Based on 27 + 14 text responses

Research

What we learned reading every model

Claude Opus 5 and xAI: Grok 4 Fast (free) have opinions about your brand too.Ask 10 models what they tell people about you. Verbatim receipts.Run the mirror

FAQ

Common questions

Keep exploring

More comparisons

xAI: Grok 4 Fast (free) vs MiniMax M3New provider

xAI: Grok 4 Fast (free) vs Gemini 2.5 Pro Preview 06-05New provider

xAI: Grok 4 Fast (free) vs GPT-5New provider