Claude Fable 5.1 and Mythos 5.1

Anthropic's new flagship models for coding and long-running knowledge work, with cache reads priced 75% lower than Fable 5.

Fable 5.1 gets further into a long task before it stops to ask you something, and Anthropic points to document, spreadsheet, and slide work as areas it improved
Fable 5.1 and Mythos 5.1 are the same underlying model with different safeguards. Fable 5.1 is the public version. Mythos 5.1 goes only to vetted cybersecurity and life-sciences organizations through restricted-access programs
Both carry a 1M-token context window at standard per-token pricing across the full window, with 128K maximum output tokens
API pricing is unchanged from Fable 5 at $10 per million input tokens and $50 per million output. Cache reads drop from $1.00 to $0.25 per million, which Anthropic says cuts typical token-billed costs by about 25%, and up to roughly 45% for heavily agentic work
Available on all plans and platforms including Amazon Web Services, Google Cloud, and Microsoft Azure. Developers call it with the model id claude-fable-5-1

Long, multi-step work you hand off and check back on later, like drafting a full report from a stack of source documents

A task runs long enough that you keep getting pulled back in to answer questions or re-supply context

Marketers running research-heavy or document-heavy projects, and teams whose AI work re-reads the same large context repeatedly

Staying informed is great. Staying ahead is better.

Pick a topic and leave with something you created.

Get new module drops and weekly AI strategy.