Exclusive: Anthropic ‘Mythos’ AI model representing ‘step change’ in power revealed in data leak
Exclusive: Anthropic ‘Mythos’ AI model representing ‘step change’ in power revealed in data leak
Publish Date: 2026-03-26 23:27:00
Source Domain: fortune.com
AI company Anthropic is developing and has begun testing with early access customers a new AI model more capable than any it has released previously, the company said, following a data leak that revealed the model’s existence.
An Anthropic spokesperson said the new model represented “a step change” in AI performance and was “the most capable we’ve built to date.” The company said the model is currently being trialed by “early access customers.”
Descriptions of the model were inadvertently stored in a publicly-accessible data cache and were reviewed by Fortune.
A draft blog post that was available in an unsecured and publicly-searchable data store prior to Thursday evening said the new model is called “Claude Mythos” and that the company believes it poses unprecedented cybersecurity risks.
The same cache of unsecured, publicly discoverable documents revealed details of a planned, invite-only CEO summit in Europe that is part of the company’s drive to sell its AI models to large corporate customers.
The AI lab left the material, including what appeared to be a draft blog post announcing a new model, in an unsecured, public data lake, according to documents separately located and reviewed by Roy Paz, a senior AI security researcher at LayerX Security, a computer and network security company, and Alexandre Pauwels, a cybersecurity researcher at the University of Cambridge.
In total, there appeared to be close to 3,000 assets linked to Anthropic’s blog that had not been published previously on the company’s news or research sites that were nonetheless publicly-accessible in this data cache, according to Pauwels, who Fortune asked to assess and review the material.
After being informed of the data leak by Fortune on Thursday, Anthropic removed the public’s ability to search the data store and retrieve documents from it.
In a statement provided to Fortune, Anthropic acknowledged that a “human error” in the configuration of…
