What is the difference between Claude Sonnet 4.5 and Claude Fable 5.1?

Both are developed by Anthropic but target different use cases. Claude Sonnet 4.5 has a 200K token context window vs Claude Fable 5.1's 1.0M. You can compare their actual outputs across 7 challenges on Rival to see how they differ in practice.

Which is better, Claude Sonnet 4.5 or Claude Fable 5.1?

It depends on your use case. Claude Sonnet 4.5 and Claude Fable 5.1 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 7 challenges so you can judge which fits your needs best.

How much does Claude Sonnet 4.5 cost compared to Claude Fable 5.1?

Claude Sonnet 4.5 costs $3/M input tokens and Claude Fable 5.1 costs $10/M input tokens. Claude Sonnet 4.5 is $7.00/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 Claude Sonnet 4.5 and Claude Fable 5.1 on Rival?

This page shows a side-by-side comparison of Claude Sonnet 4.5 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

Claude Sonnet 4.5vsClaude Fable 5.1

Claude Sonnet 4.5 is cheaper than Claude Fable 5.1 at $3/M vs $10/M input tokens.

Claude Sonnet 4.5 and Claude Fable 5.1 compared across 7 shared prompts
Spec	Claude Sonnet 4.5	Claude Fable 5.1
Input price	$3/M tokens	$10/M tokens
Output price	$15/M tokens	$50/M tokens
Context window	200K tokens	1.0M tokens
Weights	Closed	Closed
Free API (OpenRouter)	No	No
Released	Sep 2025	Sep 2026

Our Verdict

Claude Fable 5.1

Claude Sonnet 4.5Runner-up

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

Claude Sonnet 4.5 costs 3.3x less per token.

Slight edge

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Claude Sonnet 4.5

Input

$3.00

3.3× cheaper

Output

$15.00

3.3× cheaper

Claude Fable 5.1

Input

$10.00

Output

$50.00

Claude Sonnet 4.5 is cheaper on both: 3.3× input, 3.3× output.

Where to run it

8 hosts

Claude Sonnet 4.54 hosts

HostInOutContextUptime

Amazon Bedrock$3.00 in$15.00 out1M99.9% up Azure AI Foundry$3.00 in$15.00 out200k99.7% up Anthropic$3.00 in$15.00 out1M100% up Google Vertex AI$3.00 in$15.00 out1M99.8% up

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

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More comparisons

Cost per 1M tokens

8 hosts

What we learned reading every model

Common questions

What is the difference between Claude Sonnet 4.5 and Claude Fable 5.1?

Which is better, Claude Sonnet 4.5 or Claude Fable 5.1?

How much does Claude Sonnet 4.5 cost compared to Claude Fable 5.1?

How can I compare Claude Sonnet 4.5 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

8 hosts

What we learned reading every model

Common questions

What is the difference between Claude Sonnet 4.5 and Claude Fable 5.1?

Which is better, Claude Sonnet 4.5 or Claude Fable 5.1?

How much does Claude Sonnet 4.5 cost compared to Claude Fable 5.1?

How can I compare Claude Sonnet 4.5 and Claude Fable 5.1 on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages