Claude Fable 5.1 splits model access from model capability

Anthropic released Claude Fable 5.1 for general use and Claude Mythos 5.1 for vetted cyber and life-sciences access. The two configurations share the same underlying model, but Fable adds safeguards and fallback behavior for high-risk requests. API cache reads now cost $0.25 per million tokens, while input and output prices remain $10 and $50 per million tokens. Why it matters: A stronger agent does not remove the need to decide which actions it may take. Treat capability, access, fallback, and audit trails as separate product controls.

Try this: Run one representative, context-heavy task with Fable 5.1 and record cache-read cost, fallback events, tool calls, and reviewer corrections before changing a production route.