What is the difference between Claude Fable 5.1 and Mercury 2?

Claude Fable 5.1 is developed by Anthropic while Mercury 2 is developed by Inception. Claude Fable 5.1 has a 1.0M token context window vs Mercury 2's 128K. You can compare their actual outputs across 10 challenges on Rival to see how they differ in practice.

Which is better, Claude Fable 5.1 or Mercury 2?

It depends on your use case. Claude Fable 5.1 and Mercury 2 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 10 challenges so you can judge which fits your needs best.

How much does Claude Fable 5.1 cost compared to Mercury 2?

Claude Fable 5.1 costs $10/M input tokens and Mercury 2 costs $0.25/M input tokens. Mercury 2 is $9.75/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 Mercury 2 on Rival?

This page shows a side-by-side comparison of Claude Fable 5.1 and Mercury 2 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 5.1vsMercury 2

Mercury 2 is cheaper than Claude Fable 5.1 at $0.25/M vs $10/M input tokens.

Claude Fable 5.1 and Mercury 2 compared across 10 shared prompts
Spec	Claude Fable 5.1	Mercury 2
Input price	$10/M tokens	$0.25/M tokens
Output price	$50/M tokens	$0.75/M tokens
Context window	1.0M tokens	128K tokens
Weights	Closed	—
Free API (OpenRouter)	No	No
Released	Sep 2026	Mar 2026

Our Verdict

Claude Fable 5.1

Mercury 2Runner-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.

Mercury 2 costs 67x less per token.

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

Mercury 2

Input

$0.25

40× cheaper

Output

$0.75

67× cheaper

Mercury 2 is cheaper on both: 40× input, 67× output.

Where to run it

5 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

Mercury 21 host

HostInOutContextUptime

Inception$0.25 in$0.75 out128k100% 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

5 hosts

What we learned reading every model

Common questions

What is the difference between Claude Fable 5.1 and Mercury 2?

Which is better, Claude Fable 5.1 or Mercury 2?

How much does Claude Fable 5.1 cost compared to Mercury 2?

How can I compare Claude Fable 5.1 and Mercury 2 on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages

Cost per 1M tokens

5 hosts

What we learned reading every model

Common questions

What is the difference between Claude Fable 5.1 and Mercury 2?

Which is better, Claude Fable 5.1 or Mercury 2?

How much does Claude Fable 5.1 cost compared to Mercury 2?

How can I compare Claude Fable 5.1 and Mercury 2 on Rival?

More comparisons

Against the newest arrivals

Same lab, same size, long tail

Model pages