Artificial intelligence · June 2026

Claude Fable 5 and Mythos 5

A Mythos-class model released for general use, with its sibling held back.

Anthropic released Claude Fable 5 as the first Mythos-class model made safe for general use, at $10 and $50 per million tokens with a 1M context. Mythos 5 went only to vetted cyber defenders through Project Glasswing, a staged release by capability.

See it in the living tree Wikipedia Source

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 1

Claude Opus 4.7 2026

What it led to 2

Watch

Introducing Claude Fable 5Anthropic · YouTube

Related measurements

The dashed line marks when it first worked.

Best AI score on GPQA Diamond Latest: 95.8 % correct (2026) Source: Epoch AI, Capabilities & benchmarking (benchmark_data.zip, gpqa_diamond.csv); Anthropic: Claude 3 public launch (March 4, 2024)

Training compute of notable AI models Source: Epoch AI, Notable AI Models (CC BY 4.0)