What is the difference between GPT-5 Codex and xAI: Grok 4 Fast (free)?

GPT-5 Codex is developed by OpenAI while xAI: Grok 4 Fast (free) is developed by xAI. You can compare their actual outputs across 34 challenges on Rival to see how they differ in practice.

Which is better, GPT-5 Codex or xAI: Grok 4 Fast (free)?

It depends on your use case. GPT-5 Codex 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 can I compare GPT-5 Codex and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of GPT-5 Codex 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 Codex and xAI: Grok 4 Fast (free)?

GPT-5 Codex is developed by OpenAI while xAI: Grok 4 Fast (free) is developed by xAI. You can compare their actual outputs across 34 challenges on Rival to see how they differ in practice.

Which is better, GPT-5 Codex or xAI: Grok 4 Fast (free)?

It depends on your use case. GPT-5 Codex 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 can I compare GPT-5 Codex and xAI: Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of GPT-5 Codex 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 Codex vs xAI: Grok 4 Fast (free): Which Is Better?

Updated Sep 2025

Our Verdict

GPT-5 Codex

xAI: Grok 4 Fast (free)Runner-up

No community votes yet. On paper, GPT-5 Codex has the edge — bigger model tier.

Too close to call

API pricing

Cost per 1M tokens

GPT-5 Codex

Input

—

Output

—

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

61%

GPT-5 Codex uses 14.6x more emoji

GPT-5 Codex

xAI: Grok 4 Fast (free)

64%Vocabulary65%

17wSentence Length13w

0.38Hedging0.56

2.3Bold1.4

3.5Lists2.5

0.15Emoji0.00

0.49Headings1.58

0.05Transitions0.28

Based on 13 + 14 text responses

Research

What we learned reading every model

GPT-5 Codex 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 Llama 4 MaverickNew provider

xAI: Grok 4 Fast (free) vs Gemini 2.5 Pro (I/O Edition)New provider

Updated Sep 2025

Our Verdict

GPT-5 Codex

xAI: Grok 4 Fast (free)Runner-up

No community votes yet. On paper, GPT-5 Codex has the edge — bigger model tier.

Too close to call

API pricing

Cost per 1M tokens

GPT-5 Codex

Input

—

Output

—

xAI: Grok 4 Fast (free)

Input

$0.000

Output

$0.000

Writing DNA

Style Comparison

Similarity

61%

GPT-5 Codex uses 14.6x more emoji

GPT-5 Codex

xAI: Grok 4 Fast (free)

64%Vocabulary65%

17wSentence Length13w

0.38Hedging0.56

2.3Bold1.4

3.5Lists2.5

0.15Emoji0.00

0.49Headings1.58

0.05Transitions0.28

Based on 13 + 14 text responses

Research

What we learned reading every model

GPT-5 Codex 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 Llama 4 MaverickNew provider

xAI: Grok 4 Fast (free) vs Gemini 2.5 Pro (I/O Edition)New provider