Anthropic Releases Claude Fable 5 and Mythos 5 with 1M Token Context

Jul 10, 2026

Anthropic has launched Claude Fable 5, a new frontier model with strict safety guardrails, and Claude Mythos 5, which shares its capabilities but lacks the safety classifiers. Both models feature a 1 million token context window, 128,000 maximum output tokens, and are priced at $10 per million input tokens and $50 per million output tokens. Early impressions from Simon Willison describe Fable 5 as slow, expensive, but highly capable.

Why it matters: Claude Fable 5 introduces enhanced safety mechanisms for advanced AI models, including automatic fallback when guardrails are triggered.

Full story at: Simon Willison's Weblog ↗