Anthropic Says Claude Fable 5.1 Could Help Synthesise a Known Weapon
Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, 2026. Essentially, they are the same underlying model with different safeguards.Fable is generally available to the users however, like its predecessor, Mythos is accessible only to vetted cybersecurity and life science organisations. Claude Fable 5.1 and Claude Mythos 5.1 were tested for chemical and biological risk apart from cybersafety, alignment, prompt injection, agentic safety and reward hacking. \Anthropic also cleared that external testers found no critical-severity jailbreak, while acknowledging that its automated audits are less reliable especially in long-context and multi-agent settings. The release includes new transparency measures […]












