Modelpeers

Claude Mythos 5 changelog

Every change to Claude Mythos 5 that Modelpeers has recorded, newest first, each with the source it came from. The record starts Jun 9, 2026.

All (3)Releases (2)Security (1)

June 2026

Claude Fable 5 and Mythos 5

2 models from Anthropic

Security

US government directive forces suspension of Fable 5 and Mythos 5

A US government export control directive, prompted by a reported method of bypassing Fable 5 safeguards found by Amazon researchers, led Anthropic to disable Fable 5 and Mythos 5 for all customers. Other models were not affected.

Who is affected:
All users of Claude Fable 5 and Claude Mythos 5 on every surface.
Action needed:
Switch to Claude Opus 4.8 until access returns.

9 incidents are listed on the Claude Mythos 5 page. Get this changelog in a feed reader with the RSS feed.