claude-fable-5-1
A Claude Code model, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
A claude-fable-5-1 model id is recognized and becomes the fable family default, with UI text updated to Fable 5.1.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.257.
In the changelogs
9Releases whose published page names claude-fable-5-1.
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v2.1.281
Model selector config: always_on dropped, min version bumped to 2.1.280
One model entry in the bundled model selector config drops
always_onthinking and now requires Claude Code 2.1.280 or laterfound in this entry's text
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v2.1.281
Bundled model-selector sample defaults Opus 5.5 to medium effort
Built-in model data now sets Opus 5.5 to medium effort and marks Medium as Default for Opus 5.5 and Fable 5.1
found in this entry's text
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v2.1.277
Model catalog version bump and per-surface model reassignment
Bundled model catalog updated to version 629 with model reassignments across ccr, ccd, and other surfaces
found in this entry's text, named in this entry
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v2.1.263
Effort-medium nudge generalized to multiple models and effort levels
The effort-downgrade nudge now works per model instead of just one, but each model needs its own flag turned on.
found in this entry's text
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v2.1.263
Effort-medium nudge generalized to per-model remote-config gates
The effort-downgrade nudge was rebuilt to support multiple models, each hidden behind its own remote switch.
found in this entry's text
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v2.1.257
Fable 5.1 model introduced
A claude-fable-5-1 model id is recognized and becomes the fable family default, with UI text updated to Fable 5.1.
found in this entry's text, named in this entry
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v2.1.257
New model identity: Claude Fable 5.1 / Mythos 5.1
A system-prompt identity block describes Claude Fable 5.1 in a Mythos-class tier above Opus, sharing weights with Mythos 5.1.
found in this entry's text, named in this entry
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v2.1.257
'Fable 5' branding shortened to 'Fable' in usage-limit messages
Usage-limit text now says Fable limit, and fable-5-1 and mythos-5-1 aliases were added.
found in this entry's text
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v2.1.257
claude-fable-5-1 model wiring (Vertex region + gate)
claude-fable-5-1 is wired up with its own Vertex region, and fallback lists now gate on a fable51 check.
found in this entry's text, named in this entry
First cited
1The earliest release whose published evidence quoted claude-fable-5-1 was v2.1.257, 1 Sep 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
Presence across releases
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the model does. All models.