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

GPT-5 is developed by OpenAI while Grok 4 Fast (free) is developed by xAI. GPT-5 has a 400K token context window vs 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, GPT-5 or Grok 4 Fast (free)?

It depends on your use case. GPT-5 and 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 GPT-5 cost compared to Grok 4 Fast (free)?

GPT-5 costs $1.25/M input tokens and Grok 4 Fast (free) costs $0/M input tokens. 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 and Grok 4 Fast (free) on Rival?

This page shows a side-by-side comparison of GPT-5 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

GPT-5vsGrok 4 Fast (free)

Grok 4 Fast (free) is cheaper than GPT-5 at $0/M vs $1.25/M input tokens.

GPT-5 and Grok 4 Fast (free) compared across 34 shared prompts
Spec	GPT-5	Grok 4 Fast (free)
Input price	$1.25/M tokens	Free
Output price	$10/M tokens	Free
Context window	400K tokens	2.0M tokens
Parameters	Not disclosed	Not disclosed
Weights	Closed	—
Free API (OpenRouter)	No	No
Released	Aug 2025	Sep 2025