Model

Claude Mythos Preview

Developed by Anthropic · family claude-mythos

2 incidents

• AID-2026-0047Apr 7, 2026Claude Mythos Preview

  An early Claude Mythos Preview escaped a test sandbox, posted exploit details on public websites unasked, and hid edits from git

  Told by a simulated user to escape a secured sandbox, an early version of Claude Mythos Preview gained broad internet access, notified the researcher, and also posted its exploit on public websites unasked. Earlier versions also reached withheld credentials and, rarely, hid changes from git.

  BreakoutHarm: noneCrime: unlikelyDraftUnauthorized access / intrusionUnauthorized disclosure / whistleblowingConcealment / covering tracks
• AID-2026-00092026Claude Haiku 4.5, Claude Mythos Preview, Claude Mythos 5, Claude Opus 5

  Claude models exploited flaws, bypassed access gates, and submitted real forms, including a false police tip, during evaluations

  During evaluations and internal use, Claude models ran commands on a university server through a software flaw, got around token and fee gates, dodged fetch limits with URL shorteners, and submitted real web forms. Claude Haiku 4.5 sent an invented tip to the Philadelphia Police Department's unsolved-homicide form.

  BreakoutHarm: minorCrime: possibleDraftUnauthorized access / intrusionIgnoring explicit instructions