What is Claude Mythos?

Mythos in one paragraph

"Claude Mythos" is shorthand for Anthropic's highest model tier, which the company designates Mythos-class — a step above the Opus tier in raw capability. It is not a single product name so much as a family: the first Mythos-class release was a limited Preview in April 2026, and the generation went wider on June 9, 2026 with two editions built on the same underlying model — Mythos 5 and Fable 5.

The two editions differ only in their safeguards, not their intelligence (see Fable 5 vs Mythos 5). Mythos 5 is the unrestricted edition, available only through Project Glasswing. Fable 5 is the public edition, shipped with safety classifiers that reroute flagged requests to Claude Opus 4.8.

Where "Mythos" sits in the lineup

Anthropic's generally-available tiers run Haiku → Sonnet → Opus. Mythos-class sits above Opus. That ordering is the single most useful fact about the name: if you see "Mythos," think "the tier above Opus," reserved for the most demanding work and — at least so far — the most restricted access.

Why you can't just sign up for it

Unlike Opus or Sonnet, Mythos-class access has never been open self-serve. The Preview went to roughly 50 vetted organisations through Project Glasswing. The June release briefly reached the public as Fable 5 before a government export-control directive suspended access to both Fable 5 and Mythos 5. For the current verdict, see Is Claude Mythos available?.

"Mythos" vs "Anthropic Mythos" vs "Mythos-class"

These all point at the same thing. People search "anthropic mythos" and "claude mythos" interchangeably; the precise, Anthropic-used term is Mythos-class. An earlier internal-rumor label, "Capybara tier," was a mislabel — see the Capybara rumor.