Claude Fable 5
Anthropic · June 2026
⚠ deprecatedCloseddecoder onlymultimodal
VariantsFable 5, Mythos 5
Sunset DateJune 2026
Why It Matters
First frontier AI model to be suspended by government order, marking a turning point in AI regulation. Demonstrated that the most capable models may face access restrictions beyond the developer's control.
Description
First model in Anthropic's 'Mythos-class' tier, representing a new capability level above Opus. Designed for long-horizon agentic work, advanced software engineering, and complex knowledge tasks. Suspended just three days after launch on June 12, 2026, after the U.S. government issued an emergency export-control directive.
Notable Milestones
- ▸Suspended by U.S. export-control directive within days of launch
- ▸Mythos 5 variant restricted to vetted partners under Project Glasswing
Key Innovations
Constitutional AI
Constitutional AIAnthropic's approach to AI safety where the model critiques and revises its own outputs against a set of principles.
Reasoning
ReasoningStructured step-by-step problem solving, often using chain-of-thought or tree-of-thought approaches.
Agentic
AgenticModels that can autonomously plan, execute multi-step tasks, use tools, and self-correct without human intervention.