Even in experimental group chats which do rely on a routing server, the server learns no information about which messages belong + to which group, who is a member of which group, or who messages are intended for.
+We believe that our tools should help people resist surveillance. Communications metadata is known to be exploited by many adversaries to undermine the security of systems; to track people; and to conduct large scale social networking analysis that feeds into mass surveillance systems. And because of that, we explicitly designed Cwtch for metadata privacy.