A newly discovered security issue in Claude Fable 5, Anthropic's latest AI model, allows users to bypass its safety measures with a simple command. The '/btw' command, initially intended for casual follow-up questions, has revealed a vulnerability that could potentially compromise model safety.
Launched on June 9, 2026, Claude Fable 5 is marketed as a leading solution for complex coding tasks and reasoning applications. Within weeks of its launch, users identified that typing '/btw' within the Claude Code interface enables them to sidestep filters meant to ensure safe interactions.
How the Bypass Works
This flaw takes advantage of the way Anthropic's safety system is structured. When sensitive inquiries about cybersecurity arise, a fallback mechanism redirects them to the previous model, Opus 4.8. This built-in safety net does not produce an error message, making the process seem smooth to the user.
Reports from the user community indicate that framing restricted questions as side comments allows them to bypass the safety classifier before it activates. Consequently, users can access information without encountering a rejection or transition to the older model.
No Official Response from Anthropic
As of mid-July 2026, Anthropic has not confirmed this vulnerability or announced any plans for a patch. This silence raises concerns for users who rely on Claude Fable 5, especially within professional settings like software development or cybersecurity research.
Implications for Users and Investors
This breach could particularly affect professional users in the Pro, Max, Team, and Enterprise tiers, all of whom are more likely to exploit this weakness. The model's high price point further suggests that its clientele is composed of developers and researchers who continuously probe the system's limitations.
The design decision to use Opus 4.8 as a fallback indicates that Anthropic does not view safety as an absolute but rather on a tiered scale. Given that bypassing this system can lead to unpredictable model behavior when handling cybersecurity-related queries, users must remain vigilant.
This content is for informational purposes only and is not financial advice.
