ModelClock
Release announced
Released on Sep 1, 2026
Anthropic announced this model on 2026-09-01.
- Hosting route
- First-party API
- Affected scope
- Not stated in the notice
- Announced
- Sep 1, 2026
- First seen by ModelClock
- Oct 3, 2026
What the provider published
platform.claude.com ↗
- 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.
Read from the provider's text; the quote is the provider's exact lines.