Users have the option of silent/automatic degradation or a complete halt. I have it set to stop rather than degrade because I want to know when I've hit the safeguard.

From the claude settings:

> Switch models when a message is flagged

> When safeguards flag a message, automatically switch to a different model to keep chatting. When off, your session will pause instead. Applies to web and remote sessions.

FWIW I get a ton of usage out of fable and it's only happened to me once.