Mythos 5.1

Project Glasswing participants can use it for AI tasks requiring a long context window and adaptive thinking.

Availability

For Project Glasswing participants

Pricing model

$10 / $50 USD per MTok; cache reads $0.25 USD per million tokens

Deployment

hosted

Privacy

Requires 30-day data retention; not available under zero data retention unless expressly authorized by Anthropic

Licence

Not established

• Standard Use grants enable the majority of biology research and development workflows on Mythos 5.1 that are blocked in generally available models.
• High-risk Use grants can remove safeguards that block life-sciences requests, but are limited for Mythos at launch and require additional vetting. ^[1]

  We are working with the US government to make high-risk grants more broadly available for Claude Mythos, but at the time of this launch they will remain limited to a small set of entities with additional vetting.

• Mythos 5.1 is accessible to verified organizations through Anthropic’s first-party console (API usage) and Claude for Enterprise and Team plans under the LSVP beta.
• LSVP requires retention of data associated with flagged activity for 30 days and that retained data cannot be used for model training or accessed by Anthropic’s life sciences research teams.
• LSVP access to Mythos 5.1 is provided on Anthropic’s hosted surfaces (Claude.ai, Claude Science, Claude Code, and API).
• Claude Mythos 5.1 is for Project Glasswing participants. ^[2]

  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.

• Both models support a 1M token context window by default and 128k max output tokens. ^[2]

  Both models support a 1M token context window by default, 128k max output tokens, and always-on adaptive thinking , at $10 / $50 USD per MTok, the same as Claude Fable 5, with cache reads cut to $0.25 USD per MTok.

• Claude Mythos 5.1 supports always-on adaptive thinking. ^[2]

  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.

• Prompt cache reads on Claude Mythos 5.1 cost $0.25 USD per million tokens. ^[2]

  Prompt cache reads on Claude Fable 5.1 and Claude Mythos 5.1 cost $0.25 USD per million tokens: 0.025x the base input price, compared with 0.1x on other models.

• Claude Mythos 5.1 requires 30-day data retention and isn't available under zero data retention unless expressly authorized by Anthropic. ^[2]

  Like Claude Fable 5, both models require 30-day data retention and aren't available under zero data retention unless expressly authorized by Anthropic.