What is the difference between GPT-5.1 Chat and xAI: Grok 4 Fast (free)?

GPT-5.1 Chat is developed by OpenAI while xAI: Grok 4 Fast (free) is developed by xAI. GPT-5.1 Chat has a 128K token context window vs xAI: 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, GPT-5.1 Chat or xAI: Grok 4 Fast (free)?

It depends on your use case. GPT-5.1 Chat and xAI: 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 GPT-5.1 Chat cost compared to xAI: Grok 4 Fast (free)?

GPT-5.1 Chat costs $1.25/M input tokens and xAI: Grok 4 Fast (free) costs $0/M input tokens. xAI: Grok 4 Fast (free) is $1.25/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 GPT-5.1 Chat and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of GPT-5.1 Chat 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 GPT-5.1 Chat and xAI: Grok 4 Fast (free)?

GPT-5.1 Chat is developed by OpenAI while xAI: Grok 4 Fast (free) is developed by xAI. GPT-5.1 Chat has a 128K token context window vs xAI: 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, GPT-5.1 Chat or xAI: Grok 4 Fast (free)?

It depends on your use case. GPT-5.1 Chat and xAI: 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 GPT-5.1 Chat cost compared to xAI: Grok 4 Fast (free)?

GPT-5.1 Chat costs $1.25/M input tokens and xAI: Grok 4 Fast (free) costs $0/M input tokens. xAI: Grok 4 Fast (free) is $1.25/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 GPT-5.1 Chat and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of GPT-5.1 Chat 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.

GPT-5.1 Chat vs xAI: Grok 4 Fast (free): Which Is Better?

Updated Nov 2025

Our Verdict

GPT-5.1 Chat

xAI: Grok 4 Fast (free)

No community votes yet. On paper, these are closely matched - try both with your actual task to see which fits your workflow.

Too close to call

API pricing

Cost per 1M tokens

GPT-5.1 Chat

Input

$1.25

Output

$10.00

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

60%

xAI: Grok 4 Fast (free) uses 157.7x more headings

GPT-5.1 Chat

xAI: Grok 4 Fast (free)

73%Vocabulary65%

18wSentence Length13w

0.45Hedging0.56

1.1Bold1.4

2.4Lists2.5

0.00Emoji0.00

0.00Headings1.58

0.06Transitions0.28

Based on 15 + 14 text responses

Research

What we learned reading every model

GPT-5.1 Chat 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 Claude Sonnet 4New provider

GPT-5.1 Chat vs xAI: Grok 4Cross-provider

Updated Nov 2025

Our Verdict

GPT-5.1 Chat

xAI: Grok 4 Fast (free)

No community votes yet. On paper, these are closely matched - try both with your actual task to see which fits your workflow.

Too close to call

API pricing

Cost per 1M tokens

GPT-5.1 Chat

Input

$1.25

Output

$10.00

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

60%

xAI: Grok 4 Fast (free) uses 157.7x more headings

GPT-5.1 Chat

xAI: Grok 4 Fast (free)

73%Vocabulary65%

18wSentence Length13w

0.45Hedging0.56

1.1Bold1.4

2.4Lists2.5

0.00Emoji0.00

0.00Headings1.58

0.06Transitions0.28

Based on 15 + 14 text responses

Research

What we learned reading every model

GPT-5.1 Chat 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 Claude Sonnet 4New provider

GPT-5.1 Chat vs xAI: Grok 4Cross-provider