A group chat is a conversation among three or more participants. RCS group chats work like modern app chats; RCS Business Messaging, however, is one-to-one, and an agent cannot join a group.
Personal RCS group chats
Over SMS, a group text is really MMS, with compressed media and no delivery or read status. Over RCS a group chat has named participants, typing indicators, read receipts, full-resolution media and reactions, and members can be added or leave. Since iOS 18.1 an iPhone in a mixed group with Android phones uses RCS rather than dropping the whole group to MMS, which is the change most people notice first.
What this means for businesses
A verified RBM agent talks to one customer per conversation. There is no way to broadcast into a family group or to run a group conversation between a brand and several customers, and a platform that claims otherwise is describing something other than RCS. A campaign to many people is many one-to-one threads, each with its own consent and its own STOP; see RCS blasts for how that is sent at volume.
Encryption note
Google Messages end-to-end encrypts personal RCS group chats between its own users; business conversations are protected in transit rather than end to end.