Anthropic Launches Fable 5 and Raises Concerns Over DeFi Security

Anthropic has released Claude Fable 5, the first publicly available AI model from the so-called Mythos class. The launch is drawing significant attention, as experts fear that powerful models of this kind could dramatically accelerate the discovery of vulnerabilities in DeFi protocols, privacy coins and smart contracts.

Built-in safety routing aims to limit risks

Because Anthropic is aware of the risks associated with a model at this level, Fable 5 includes an automatic safety routing mechanism. As soon as a user asks a question about cyberattacks, biological or chemical threats, or model replication, the system automatically routes that query to the less advanced Claude Opus 4.8.

This is not just any model. Opus 4.8 previously played a role in identifying a critical vulnerability in the Orchard protocol of Zcash. That immediately underscores how serious even the less powerful variants already are when it comes to analysing complex cryptographic code.

Alongside Fable 5, Anthropic is also announcing Claude Mythos 5, but for now that model is only available to a small group of cybersecurity specialists and critical infrastructure providers. Mythos 5 shares the same underlying model as Fable 5, but the safety restrictions have been lifted in certain areas.

Double-edged sword for the crypto world

The launch of Fable 5 is a double-edged sword for the crypto sector. On one hand, AI models at this level can be used for automated audits of smart contracts and DeFi protocols, which could significantly improve the security of those systems. On the other hand, that same capability also increases the risk that malicious actors will find vulnerabilities more quickly in code that has not yet been audited.

That concern is not hypothetical. Recently, the Humanity Protocol was hit by a major hack in which $36 million was stolen, showing just how vulnerable protocols can be. The more powerful the AI tools available to both hackers and auditors, the greater the importance of thorough code reviews before a project goes live. The launch of Fable 5 has put that discussion sharply back on the agenda.