Anthropic releases Claude Fable 5, based on the rewritten Mythos model
Anthropic has launched Claude Fable 5, a public version of its rewritten Mythos model. The model sets new records in complex tasks but includes stringent security guardrails.
What happened?
AI company Anthropic has launched Claude Fable 5, the first public and security-adapted version of their rewritten model, Mythos. The model is specifically designed to handle long and complex workflows in software development, knowledge work, and image analysis. To prevent misuse, Anthropic has included guardrails that cause the model to automatically refuse to answer questions related to cybersecurity risks and biological threats.
Key facts
| Modellnamn | Claude Fable 5 (baserad på Mythos) |
|---|---|
| Lanseringsdatum | 9 juni 2026 |
| Hex Benchmark-resultat | Över 90 % (10 procentenheters ökning) |
| Utvecklare | Anthropic |
Why it matters
The model represents a significant leap forward for Anthropic in its ability to perform autonomous, long-running tasks without losing context. By limiting the model's knowledge in sensitive areas such as biosafety and malicious code, Anthropic is simultaneously setting a new standard for how powerful AI models can be commercialised safely.
Who is affected?
The launch primarily concerns software developers, data analysts, and companies building advanced AI services. Organizations with high requirements for IT security and ethics will also be positively affected by the model's built-in limitations regarding high-risk topics.
Impact on the EU
Claude Fable 5 is being launched globally and is available to developers and companies in both the EU and the US via Anthropic's API and platforms. Because the model lacks the capacity to handle cybersecurity and biology-related queries, it meets the strict safety and risk requirements under the EU AI Act.
What else you should know
During the test phase, analysis firm Hex showed that Fable 5 achieved over 90 percent on their benchmark for complex, long-running analysis tasks—a 10 percentage point increase compared to previous top models. Developers wishing to use the model can access it directly via the Anthropic developer portal.
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