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Anthropic rolls out public version of Mythos without cybersecurity capability

By Thomson Reuters Jun 9, 2026 | 12:01 PM

By Deepa Seetharaman and Zaheer Kachwala

June 9 (Reuters) – Anthropic is rolling out a public version of its Mythos AI model, but with guardrails barring its use in risky areas ​such as cybersecurity, after a preview earlier this year sent ‌shockwaves globally with its ability to find software flaws.

The new Claude Fable 5 is the most powerful model Anthropic has ever made for wider use, the startup said on Tuesday, touting its performance in software engineering and analytics.

Anthropic has ‌so ​far limited its access to a group ⁠of about 200 organizations including ⁠the U.S. government under the Glasswing program, after announcing in April that Mythos had uncovered thousands of software vulnerabilities.

Offering its capabilities more widely may allow the $965 billion company to extend the momentum ​that has powered its valuation above rival OpenAI just as the two startups at the center of the AI industry race ⁠to go public.

The company said it had ⁠done extensive testing to ensure that users could ​not manipulate the new model to bypass its guidelines and perform restricted ​actions.

“Let’s say I’m a college student asking the model like ‌help me find cyber vulnerabilities on X package or code. The model would refuse and Fable 5 will fall back to Opus 4.8 for a response,” Dianne Penn, Anthropic’s head of product management, research ⁠and labs, told Reuters.

Fable 5 will be a more expensive model, but it accomplishes tasks with lower token usage, bringing the overall cost per ⁠task down, according ‌to early customer feedback, Penn said.

Anthropic also said ⁠users who had access to the preview version of ​Claude ‌Mythos, the version without guardrails, would be able ​to upgrade ⁠to the new Claude Mythos 5.

The company said it planned to expand access over time through a more “systematic trusted-access program.”

Pricing on both models is $10 per million input tokens and $50 per million output tokens, the company said.

(Reporting by Zaheer Kachwala in Bengaluru and Deepa Seetharaman in San Francisco; Editing ​by Anil D’Silva)