Data leak reveals Anthropic's 'Mythos' model, a 'step change' beyond Opus

Miles_Brundage · x · 2026-09-26

Fortune reports 3,000 unpublished Anthropic assets were found in an unsecured, publicly searchable data store, including a draft post about "Claude Mythos," a new tier above Opus.
Anthropic confirmed it is developing and already testing with early-access customers a new model it calls a "step change" and the "most capable we've built to date," with the draft flagging unprecedented cybersecurity risks.
The exposure was accidental; the company has acknowledged the testing program. Miles Brundage amplified the story.

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