Notifications of credits running now work like so:
How will I know that my domain has reached a credit limit?
Admins will receive an email warning and in-product banner when the account has reached 80% of their credit limit threshold and another email when they reach 100% of their credit limit.
From: Asana Help Center
I think 80% is too close to the credit limit to be a meaningful warning, especially since this warning is sent to admins, and not directly to the people utilising AI Studio rules.
In general I think credit consumption should become more transparent, not just to admins but also to users.
Adding a notification at 50% credit consumption seems the simplest improvement to start with.