Release dates
— Claude Fable 5.1 reached general availability; the same underlying model is offered as Claude Mythos 5.1 through trusted access programs. ↗
Claude Fable 5.1
The successor to Fable 5 for long-horizon agents, coding, research, and complex knowledge work, released with more precise cybersecurity and biology safeguards.
MODEL NUMBER086
- First public date
- 2026-09-01
- Organization
- Anthropic
- Family
- Claude
01
Specifications
Only published specifications are shown.
02
Overview
Why it mattered
Fable 5.1 makes Mythos-class capability generally available behind safeguards, combining more precise protections, lower cache-read pricing, and stronger long-horizon work in the Fable line.
PreviousClaude Fable 5— · — ctx
CurrentClaude Fable 5.1— · 1M ctx
04
Architecture & capabilities
Model capabilities
Adaptive reasoningLong-horizon agentCoding
Connected tools
Computer use
Product features
ResearchProfessional work
Unclassified tags
Adaptive safeguards
05
Release history
Claude Fable 5.1 reached general availability; the same underlying model is offered as Claude Mythos 5.1 through trusted access programs.
View source06
Related models
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07
Sources
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