Not sure why people thinks it’s a fork. RCS is only a standard, there is no open source implementation. Even to use it commercially you need to license it from GSMA. So every implementation of RCS is proprietary for the server side. On client side, Google has published the code in Android 12 sources. But most clients are all proprietary too.
Where it belongs. Google's fork of the open RCS standard is closed source and proprietary.
> Google's version of RCS—the one promoted on the website with Google-exclusive features like optional encryption—is definitely proprietary, by the way. If this is supposed to be a standard, there's no way for a third-party to use Google's RCS APIs right now. Some messaging apps, like Beeper, have asked Google about integrating RCS and were told there's no public RCS API and no plans to build one.
https://arstechnica.com/gadgets/2022/08/new-google-site-begs...