From cybersecurity to biology and chemistry, all the things Claude Fable 5 AI can't do for you

Published 10 June 2026 · tech

Anthropic has just launched Claude Fable 5, a new AI model that the company describes as a Mythos-class system made available for general use. What

Anthropic has just launched Claude Fable 5, a new AI model that the company describes as a Mythos-class system made available for general use. What makes the launch particularly interesting is that Anthropic says Fable 5 exceeds the capabilities of all of its generally available AI models to date. According to the company, the model has delivered exceptional results across a wide range of AI benchmarks and has shown strong performance in software engineering, knowledge work, scientific research, vision tasks and many other areas. Read Full Story But there is a catch. Anthropic says the model's advanced capabilities also come with risks that could potentially be misused to cause serious harm. As a result, the company has launched Fable 5 with a new set of safeguards designed to reliably prevent misuse, even in cases involving sophisticated attempts to bypass the model's restrictions. The company says these safeguards are intended to prevent Fable 5 from providing information or advice that could help malicious actors cause serious harm that they could not easily obtain elsewhere. To achieve this, Anthropic has introduced a new layer of classifiers: separate AI systems that monitor requests, detect potential misuse, identify jailbreak attempts and block unsafe responses before they are generated.

In some sensitive areas, Fable 5 does not respond at all. Instead, requests are automatically routed to Claude Opus 4.8, which operates under a different safety framework. So what exactly can Anthropic's newest AI model not do? 1. It won't help you with offensive cybersecurity tasks One of the biggest concerns surrounding highly capable AI systems is their potential use in cyberattacks. Mythos-class models are known for their ability to discover and exploit software vulnerabilities. Because of this, Anthropic says it has implemented specialized cybersecurity safeguards in Fable 5. The company claims its cybersecurity classifiers cover a broad range of exploitation and offensive cyber activities. If users attempt to use Fable 5 for these purposes, the safeguards are designed to stop the model from making meaningful progress on such tasks. In simple terms, if someone tries to use Fable 5 as a hacking assistant, Anthropic wants the model to refuse. 2. It won't freely assist with biology and chemistry research Anthropic has also expanded restrictions around biology and chemistry. Previous Claude models already blocked a relatively narrow set of bioweapons-related requests. However, the company says Fable 5's stronger scientific capabilities required a broader approach.