Google is preparing to integrate Google Messages RCS to work with Samsung’s Continuity feature. This feature lets Samsung Tablet and Smartwatch users receive calls and messages from a Samsung smartphone. The new integration would let the Continuity feature access incoming RCS messages and let users respond while using Google Messages.
Samsung Galaxy S21 Ultra
XDA-Developers discovered this through the strings of text contained in the Android Messages app code. The text refers to a new permission within the app.
Permission to send SMS/MMS/RCS messages using Android Messages API
With this permission the app will be allowed to send SMS/MMS/RCS using Android Messages. It will have an access to send messages with any extra approvals.
It was initially reported that Google Messages was opening an API for third-party apps to handle RCS messaging, but it was later verified that the particular build of Google Messages containing this text is present solely in the Google Messages build for Samsung smartphones.
The permission is being built specifically because Samsung (outside the US) uses Google Messages as the default out-of-the-box messaging app. Before that, Samsung used its own One UI app for SMS and it indeed supported RCS messaging as well.