Cognition just added Claude Fable 5 to its entire Devin lineup. The model is now live in Devin Cloud, Devin Desktop, and Devin CLI , and according to Cognition's own benchmark, it's the best model available for real-world engineering tasks.

The timing is notable. Anthropic announced Claude Fable 5 as a Mythos-class model available to enterprise customers and paid subscribers just today, and Devin is already shipping it across every product tier. Fable 5 is a Mythos-class model made safe for general use, with capabilities that exceed any model Anthropic has ever made generally available, showing exceptional performance in software engineering, knowledge work, vision, and scientific research.

What Mythos-class actually means

To understand why this matters, a bit of context: Mythos-class models are a tier of Claude models that sit above the Opus class in capability. The first, Claude Mythos Preview, was released through Project Glasswing. That preview was gated to a handful of cybersecurity partners because of its advanced ability to find and exploit vulnerabilities. Fable 5 is the public-safe version of that same tier , it uses the same tier of technology as Mythos but is safe for use by the public because of safeguards and limits placed on the technology.

In high-risk areas like cybersecurity, biology, chemistry, and distillation, the model blocks responses and falls back to Claude Opus 4.8. These safeguards trigger, on average, in less than 5% of sessions. For most engineering workflows , the kind Devin handles , you'll never notice the guardrails.