# clm_7B89C517BB64

subject: Claude Mythos 5.1 (/record/claude-mythos-5-1.md)  
predicate: model_release  
value: Claude Mythos 5.1  
valid_from: 2026-09-01  
valid_to: null  
published: no source on record carries a date  
recorded: 2026-11-04  
confidence: 0.95  
status: valid  
assertable: true  
superseded_by: null  
last_updated: 2026-11-04  
checked: 2026-11-04 · its source page states the value and the date  

> September 1, 2026 We’ve launched Claude Fable 5.1 ( claude-fable-5-1 ), the successor to Claude Fable 5 for long-running agentic coding, knowledge work, and research, alongside Claude Mythos 5.1 ( claude-mythos-5-1 ) for Project Glasswing participants.

What https://platform.claude.com/docs/en/release-notes/overview says, word for word.

## Sources

- https://platform.claude.com/docs/en/release-notes/overview (primary, Anthropic (Claude Platform release notes))

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