PCMag editors select and review products independently. If you buy through affiliate links, we may earn commissions, which help support our testing.

Anthropic’s New Mythos Model Reportedly Accessed By Unauthorized Users

The AI company previously said its latest model would be limited to select companies for testing purposes.

 & James Peckham Reporter

Our team tests, rates, and reviews more than 1,500 products each year to help you make better buying decisions and get more from technology.

Our Expert
LOOK INSIDE PC LABS HOW WE TEST
65 EXPERTS
43 YEARS
41,500+ REVIEWS
(Credit: Samuel Boivin/NurPhoto via Getty Images)

In early April, Anthropic announced its latest Mythos model, saying it would remain exclusive to select tech companies for cybersecurity purposes. Anthropic has now confirmed it's actively investigating an incident where a group claims to have unauthorized access to Mythos.

A Bloomberg report, citing anonymous sources, documentation, and examples of Mythos up and running, alleges that a group of users accessed the Mythos model without Anthropic’s authorization.

Mythos is said to be capable of exploiting vulnerabilities in “every major operating system and every major web browser," if the user intends to do so, according to Anthropic.

At launch, Anthropic claimed to have found “thousands of high-severity vulnerabilities” in everyday software. Yesterday, Mozilla claimed to have found 271 vulnerabilities within Firefox through its use of Mythos.

Anthropic previously said it would restrict access to the model to 11 tech companies through its Project Glasswing program. Restricting users means software makers can fix any identified software issues before bad actors gain access to similar AI models.

However, that exclusivity may not have been as strong as first thought, with this group of users who talk in a private Discord group claiming to have had access since day one. If true, they've had access to the software for over two weeks.

The group told Bloomberg that it accessed the tool through a member's third-party contractor status with Anthropic. It also used tools typically employed by cybersecurity researchers, along with knowledge of where Anthropic hosts other models, to better predict where Mythos would sit within its systems.

A spokesperson for Anthropic told Bloomberg, “We’re investigating a report claiming unauthorized access to Claude Mythos Preview through one of our third-party vendor environments.” It says there’s currently no evidence that access went beyond the vendor’s own tools.

Speaking with Bloomberg, the group says it's not intending to cause any damage with its access to Mythos. That may not be true for other groups who may be trying to gain access to Mythos themselves.

About Our Expert

James Peckham

James Peckham

Reporter

I’ve been a journalist for over a decade after getting my start in tech reporting back in 2013. I joined PCMag in 2025, where I cover the latest developments across the tech sphere, writing about the gadgets and services you use every day. Be sure to send me any tips you think PCMag would be interested in.

I’ve worked at TechRadar, Android Police, T3, and more, where I broke many tech stories you may have read, including the return of the Motorola Razr when it first became a foldable phone. Based near London, I’ve appeared on BBC News, Al Jazeera, and other TV networks, podcasts, and radio shows as an expert on the latest tech stories and trends.

Read full bio