Claude Mythos Preview changelog

Every change to Claude Mythos Preview that Modelpeers has recorded, newest first, each with the source it came from. The record starts Apr 7, 2026.

All (2)Releases (1)Retiring (1)

June 2026

Claude Mythos Preview

Model at Anthropic

RetiringJun 9, 2026

Claude Mythos Preview deprecated, retirement date to be announced

The model deprecations table lists claude-mythos-preview as deprecated on June 9, 2026, the day Mythos 5 launched as its upgrade. No retirement date has been set.

Who is affected:: Project Glasswing partners using Claude Mythos Preview.
What to do:: Plan a move to Claude Mythos 5.1.

April 2026

Claude Mythos Preview

Model at Anthropic

New releaseApr 7, 2026

Claude Mythos Preview opens as a gated research preview

Anthropic made Claude Mythos Preview available as an invitation-only research preview for defensive cybersecurity work through Project Glasswing.

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