What classifies a number in imessages as a known number? In iOS 26 what makes a number filtered out of the main inbox?

With the new ios 26 update, certain numbers will be filtered into other inboxes within imessage. What numbers are classified as "known", and will not be moved into these filters. Do they need to be a contact in your phone, or if a business texts you how will that be filtered?

What classifies a number in imessages as a known number? In iOS 26 what makes a number filtered out of the main inbox?
 
 
Q