Anthropic unveiled its latest AI, Claude Fable 5, positioning it as a Mythos-class model engineered for broad public access while incorporating stringent safety measures. Unlike the more powerful Mythos 5, which remains restricted due to its potential misuse in cybersecurity exploits, Fable 5 aims to provide advanced capabilities across diverse tasks but blocks sensitive queries related to cybersecurity, biology, chemistry, and AI distillation.
The company stresses that Fable 5 excels in complex and extended tasks, surpassing previous public releases on benchmarks involving software engineering, vision-related functions, knowledge work, and research. Despite these achievements, certain high-risk functions are deliberately rerouted to Anthropic’s Opus 4.8 model, ensuring that security-sensitive operations remain tightly controlled.
Mythos 5, referenced as a less restricted counterpart to Fable 5, is currently available only to select testers and government entities within Anthropic’s "Project Glasswing" initiative. This cautious rollout follows concerns that earlier versions of Mythos demonstrated capabilities to detect software vulnerabilities so effectively they could enable large-scale cyberattacks if misused.
Benchmark data shared by Anthropic shows that both Fable 5 and Mythos 5 outperform competitors including Mythos Preview, OpenAI's GPT-5.5, Google's Gemini 3.1 Pro, and Anthropic’s own Opus 4.8 across multiple domains. They lead in agentic coding, legal reasoning, multidisciplinary problem-solving without tools, spatial reasoning, and healthcare-related tasks. Meanwhile, Mythos Preview holds a slight edge in multitasking with external tools and computer use, although Fable 5 claims a comprehensive advantage overall.
This release reflects Anthropic’s strategy to balance AI advancement with ethical safeguards. Fable 5 offers powerful language and task capacity for enterprises, developers, and general users without exposing them to the security risks linked to unfettered access to vulnerabilities in digital infrastructure.