Claude Opus 4.5 vs Claude Fable 5.1

Pyyan / Compare / Claude Opus 4.5 vs Claude Fable 5.1

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Language Models · verified 2 Sept 2026

Claude Opus 4.5Anthropicdeprecated

Claude Fable 5.1Anthropiccurrent

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Specification	Claude Opus 4.5	Claude Fable 5.1
Summary	Legacy Opus, still callable.	Same price as Fable 5, and cache reads cost a quarter of what they did.
Context	—	1M
Input ($/Mtok)	—	$10
Output ($/Mtok)	—	$50
Licence	Proprietary	Proprietary
Max output	—	128K
Parameters	—	Not published
Released	—	1 Sep 2026
Model ID	claude-opus-4-5	claude-fable-5-1
Category	Language Models	Language Models
Official	Anthropic ↗	—

Highlighted rows are where these differ.

Legacy Opus, still callable.

Best for pinned workloads.

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.