Claude Mythos 5.1
The same model as Claude Fable 5.1, offered by invitation only through Project Glasswing for vetted cybersecurity-defense and life-sciences work that Anthropic's public safeguards would otherwise block
Claude Mythos 5.1
Anthropic • September 2026
Training Data
Up to June 2026
Claude Mythos 5.1
September 2026
Parameters
Not disclosed
Training Method
Same weights as Fable 5.1, deployed under a vetted-access safeguard regime with always-on adaptive thinking
Context Window
1,000,000 tokens
Knowledge Cutoff
June 2026
Key Features
Project Glasswing Only • Same Model as Fable 5.1 • 1M Context / 128K Output
Capabilities
Security: Outstanding
Life Sciences: Outstanding
Reasoning: Outstanding
What's New in This Version
Fable 5.1's capabilities with the cyber and biology safeguards relaxed for approved organizations — threat intelligence, vulnerability discovery, red teaming, drug discovery, and biodefense screening; $10/$50 per 1M tokens, with access limited to selected US organizations
The same model as Claude Fable 5.1, offered by invitation only through Project Glasswing for vetted cybersecurity-defense and life-sciences work that Anthropic's public safeguards would otherwise block
What's New in This Version
Fable 5.1's capabilities with the cyber and biology safeguards relaxed for approved organizations — threat intelligence, vulnerability discovery, red teaming, drug discovery, and biodefense screening; $10/$50 per 1M tokens, with access limited to selected US organizations
Technical Specifications
Key Features
Capabilities
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