New Anthropic Fable 5 Is a “Mythos-Class” LLM Available to All
New Anthropic Fable 5 Is a “Mythos-Class” LLM Available to All
https://www.infosecurity-magazine.com/news/fable-5-mythos-class-anthropic/
Publish Date: 2026-06-10 07:00:00
Source Domain: www.infosecurity-magazine.com
Just days after expanding its cybersecurity-focused frontier AI program, Project Glasswing, Anthropic released two new models, Claude Mythos 5 and Claude Fable 5.
Mythos 5 has been presented by Anthropic as “an upgrade to Claude Mythos Preview” and the AI company claimed in a June 9 announcement that it has “the strongest cybersecurity capabilities of any model in the world.”
This new upgrade will initially be deployed through Project Glasswing, in collaboration with the US government, but the company plans for a wider availability of the model in the future via “a broader trusted access program.”
Meanwhile, Fable 5 has is said to be powered by the same underlying frontier AI model as Mythos 5 but with additional guardrails, especially in areas like cybersecurity where the company said it “could be misused to cause serious damage.”
One of these safeguards involves a system where queries made by Fable 5 on certain topics will receive a response from Claude Opus 4.8, Anthropic’s next-in-line model that is available to everyone.
“To release the model both safely and quickly, we’ve tuned these safeguards conservatively – they’ll sometimes catch harmless requests, though they trigger, on average, in less than 5% of sessions,” cautioned the AI company, adding that is it working on new models where these safeguards will be fine-tuned to reduce false positives.
Fable 5 and Mythos 5 are being offered at $10 per million input tokens and $50 per million output tokens, less than half the price of Claude Mythos Preview at $25 per million input tokens and $125 per million output tokens.
Quickly following the Anthropic announcement, Microsoft said Fable 5 is now available in Microsoft Foundry and can be used to power agents in GitHub Copilot and Foundry Agent Service.
Fable’s Guardrails May Not Be Sufficient, Cyber Experts Warn
The Anthropic announcement generated mixed feelings in the cybersecurity industry.
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