Official support for Google Messages on GrapheneOS is being developed instead of needing to set it up in a very particular way where it can be fragile. In the long term, we plan to make our own RCS app.

you need the google messaging app for RCS

Is it because no one else has tried implementing the RCS standard or because Google has some proprietary hold over it?

No one else has tried implementing the RCS standard.

There just aren't any open-source Android libraries for RCS out there, much less anything in AOSP.

https://github.com/search?q=rcs+android&type=repositories

Apple has RCS, compatible with Android, at least in the EU. You don't get the blue bubble though.

I think they’re asking about on Android. The point is whether there’s an alternative RCS client to run on GOS.

Which itself is not guaranteed to work even on ”stock” Android, let alone GOS — which multiple people (myself included) have been experiencing firsthand.

GrapheneOS hasn't added official support for it yet, but we're working on it. People using it on GrapheneOS have been relying on it working for many people with various tweaks but not everyone. Official support will make it reliable.

Are you going to do it by making Google Messages to work, or by building an another RCS client implementation?

I'm also curious about the answer to this. An open-source third-party RCS implementation would be a massive boon to the ecosystem. It's obviously theoretically possible for non-Google-Messages SMS apps to support RCS (since vendors like Samsung were able to add it to theirs before deprecating it in favor of Google Messages), but it sounds like that's a non-trivial task (which is probably why said vendors ended up deprecating theirs in favor of Google Messages).

Both, but first adding official support for using Google Messages.

RCS is an abomination.