Google’s the main backer but it’s technically an open standard. Apple is implementing support in iOS 18 too, reluctantly. Google also has non-standard extensions on top of it like e2e encryption. I wish they would standardize it but that’s a pretty important feature and maybe it’s ok that they brought it out before it could become standard.
I've got RCS disabled so hopefully it doesn't. I got a new Android phone which had it unfortunately enabled by default which caused a bunch of messages to not reach their destination.