Anthropic's Fable 5 returns after two-week ban over jailbreak discovery

Key takeaway

• Anthropic's Fable 5 has returned globally after a two-week US government ban triggered by a security discovery.

• Amazon researchers found a method to bypass the model's safety guardrails, causing it to identify software vulnerabilities and demonstrate exploit code.

• Though Anthropic deployed a classifier blocking the technique in over 99 percent of cases, the company acknowledges that making AI models fully resistant to jailbreaks is likely impossible, suggesting that security review and government oversight will remain standard practice for powerful AI systems.

3 Key Points

FAQ

When is Fable 5 available again, and what are the pricing terms?

Fable 5 is back worldwide starting today through Claude Platform, Claude.ai, Claude Code, and Claude Cowork. Pro, Max, Team, and select Enterprise plans include the model through July 7 at up to 50 percent of weekly usage limits; after that, it will be billed through usage credits.

What was the security issue that triggered the ban?

Amazon researchers discovered a way to bypass Fable 5's safety guardrails. Once bypassed, the model identified several software vulnerabilities and in one case produced code showing how to exploit one of them. Anthropic trained an improved safety classifier that blocks that specific technique in more than 99 percent of cases.

Will Mythos 5 become more widely available?

Mythos 5, the less restricted version of the same base model, currently remains limited to a group of US organizations that received government approval on June 26. Anthropic says it is still working with the government to expand access to more partners in the Glasswing program, though whether the EU will join remains unclear.