Claude Mythos 5.1 vs Claude Fable 5.1

Pyyan / Compare / Claude Mythos 5.1 vs Claude Fable 5.1

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Language Models · verified 2 Sept 2026

Claude Mythos 5.1Anthropiccurrent

Claude Fable 5.1Anthropiccurrent

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Specification	Claude Mythos 5.1	Claude Fable 5.1
Summary	Fable 5.1 with the safety classifiers removed. You cannot simply buy it.	Same price as Fable 5, and cache reads cost a quarter of what they did.
Context	1M	1M
Input ($/Mtok)	$10	$10
Output ($/Mtok)	$50	$50
Licence	Proprietary, gated	Proprietary
Max output	128K	128K
Parameters	Not published	Not published
Released	1 Sep 2026	1 Sep 2026
Model ID	claude-mythos-5-1	claude-fable-5-1
Category	Language Models	Language Models
Official	—	—

Highlighted rows are where these differ.

The same underlying model as Fable 5.1, at a different safeguard level
US organisations and individuals in Anthropic's trusted access programmes only
Safety classifiers and high-risk fallbacks removed for Project Glasswing participants

Best for vetted frontier research.

Matches or beats Fable 5 at low and medium effort, and pulls clear at high effort
Cache reads cut to 25% of the old price, so re-reading a long context got much cheaper
Identical model to Mythos 5.1 underneath; the difference is the safeguards

Best for coding and long-running work.