What is the difference between Claude Fable 5.1 and Horizon Alpha?

Claude Fable 5.1 is developed by Anthropic while Horizon Alpha is developed by OpenRouter. Claude Fable 5.1 has a 1.0M token context window vs Horizon Alpha's 256K. You can compare their actual outputs across 5 challenges on Rival to see how they differ in practice.

Which is better, Claude Fable 5.1 or Horizon Alpha?

It depends on your use case. Claude Fable 5.1 and Horizon Alpha each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 5 challenges so you can judge which fits your needs best.

How much does Claude Fable 5.1 cost compared to Horizon Alpha?

Claude Fable 5.1 costs $10/M input tokens and Horizon Alpha costs $0/M input tokens. Horizon Alpha 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 Claude Fable 5.1 and Horizon Alpha on Rival?

This page shows a side-by-side comparison of Claude Fable 5.1 and Horizon Alpha 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 Fable 5.1vsHorizon Alpha

Horizon Alpha is cheaper than Claude Fable 5.1 at $0/M vs $10/M input tokens.

Claude Fable 5.1 and Horizon Alpha compared across 5 shared prompts
Spec	Claude Fable 5.1	Horizon Alpha
Input price	$10/M tokens	Free
Output price	$50/M tokens	Free
Context window	1.0M tokens	256K tokens
Weights	Closed	—
Free API (OpenRouter)	No	No
Released	Sep 2026	Jul 2025

Our Verdict

Claude Fable 5.1

Horizon AlphaRunner-up

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

Slight edge

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Claude Fable 5.1

Input

$10.00

Output

$50.00

Horizon Alpha

Input

$0.000

Output

$0.000

Where to run it

4 hosts

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

Horizon Alpha

No hosts listed on OpenRouter.

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 Claude Fable 5.1 and Horizon Alpha?

Which is better, Claude Fable 5.1 or Horizon Alpha?

How much does Claude Fable 5.1 cost compared to Horizon Alpha?

How can I compare Claude Fable 5.1 and Horizon Alpha 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 Claude Fable 5.1 and Horizon Alpha?

Which is better, Claude Fable 5.1 or Horizon Alpha?

How much does Claude Fable 5.1 cost compared to Horizon Alpha?

How can I compare Claude Fable 5.1 and Horizon Alpha on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages