What is the difference between ChatGPT-4o (March 2025) and Claude Fable 5.1?

ChatGPT-4o (March 2025) is developed by OpenAI while Claude Fable 5.1 is developed by Anthropic. ChatGPT-4o (March 2025) has a 128K token context window vs Claude Fable 5.1's 1.0M. You can compare their actual outputs across 4 challenges on Rival to see how they differ in practice.

Which is better, ChatGPT-4o (March 2025) or Claude Fable 5.1?

It depends on your use case. ChatGPT-4o (March 2025) and Claude Fable 5.1 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 4 challenges so you can judge which fits your needs best.

How much does ChatGPT-4o (March 2025) cost compared to Claude Fable 5.1?

ChatGPT-4o (March 2025) costs $5/M input tokens and Claude Fable 5.1 costs $10/M input tokens. ChatGPT-4o (March 2025) 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 ChatGPT-4o (March 2025) and Claude Fable 5.1 on Rival?

This page shows a side-by-side comparison of ChatGPT-4o (March 2025) and Claude Fable 5.1 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 2026

ChatGPT-4o (March 2025)vsClaude Fable 5.1

ChatGPT-4o (March 2025) is cheaper than Claude Fable 5.1 at $5/M vs $10/M input tokens.

ChatGPT-4o (March 2025) and Claude Fable 5.1 compared across 4 shared prompts
Spec	ChatGPT-4o (March 2025)	Claude Fable 5.1
Input price	$5/M tokens	$10/M tokens
Output price	$15/M tokens	$50/M tokens
Context window	128K tokens	1.0M tokens
Weights	—	Closed
Free API (OpenRouter)	No	No
Released	Mar 2025	Sep 2026

Our Verdict

Claude Fable 5.1

ChatGPT-4o (March 2025)Runner-up

Not enough votes to call it. On the specs, Claude Fable 5.1 has the edge: newer, bigger context window.

ChatGPT-4o (March 2025) costs 3.3x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

ChatGPT-4o (March 2025)

Input

$5.00

2.0× cheaper

Output

$15.00

3.3× cheaper

Claude Fable 5.1

Input

$10.00

Output

$50.00

ChatGPT-4o (March 2025) is cheaper on both: 2.0× input, 3.3× output.

Where to run it

4 hosts

ChatGPT-4o (March 2025)

No hosts listed on OpenRouter.

Claude Fable 5.14 hosts

HostInOutContextUptime

Amazon Bedrock$10.00 in$50.00 out1M—Anthropic$10.00 in$50.00 out1M99.1% up Azure AI Foundry$10.00 in$50.00 out1M99.1% up Google Vertex AI$10.00 in$50.00 out1M99.8% up

Per million tokens. Prices and uptime via OpenRouter, checked 16 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

Keep exploring

More comparisons

Cost per 1M tokens

4 hosts

What we learned reading every model

Common questions

What is the difference between ChatGPT-4o (March 2025) and Claude Fable 5.1?

Which is better, ChatGPT-4o (March 2025) or Claude Fable 5.1?

How much does ChatGPT-4o (March 2025) cost compared to Claude Fable 5.1?

How can I compare ChatGPT-4o (March 2025) and Claude Fable 5.1 on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages

Cost per 1M tokens

4 hosts

What we learned reading every model

Common questions

What is the difference between ChatGPT-4o (March 2025) and Claude Fable 5.1?

Which is better, ChatGPT-4o (March 2025) or Claude Fable 5.1?

How much does ChatGPT-4o (March 2025) cost compared to Claude Fable 5.1?

How can I compare ChatGPT-4o (March 2025) and Claude Fable 5.1 on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages