What is the difference between Grok 4 Fast (free) and OpenAI o3?

Grok 4 Fast (free) is developed by xAI while OpenAI o3 is developed by OpenAI. You can compare their actual outputs across 35 challenges on Rival to see how they differ in practice.

Which is better, Grok 4 Fast (free) or OpenAI o3?

It depends on your use case. Grok 4 Fast (free) and OpenAI o3 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 Grok 4 Fast (free) cost compared to OpenAI o3?

Grok 4 Fast (free) costs $0/M input tokens and OpenAI o3 costs $10/M input tokens. Grok 4 Fast (free) is $10.00/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 Grok 4 Fast (free) and OpenAI o3 on Rival?

This page shows a side-by-side comparison of Grok 4 Fast (free) and OpenAI o3 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

Grok 4 Fast (free)vsOpenAI o3

Grok 4 Fast (free) is cheaper than OpenAI o3 at $0/M vs $10/M input tokens.

Grok 4 Fast (free) and OpenAI o3 compared across 35 shared prompts
Spec	Grok 4 Fast (free)	OpenAI o3
Input price	Free	$10/M tokens
Output price	Free	$40/M tokens
Context window	2.0M tokens	—
Parameters	Not disclosed	Not disclosed
Weights	—	Closed
Free API (OpenRouter)	No	No
Released	Sep 2025	Apr 2025