Yes it is, it’s been developed by the GSM Association, but Google does have de facto monopoly in the market right now by their Jio Jibe virtual carrier. RCS can be freely implemented by carriers and device manufacturers independently of that, but so far only Samsung, T-Mobile USA and Verizon did so — everyone else uses Google’s Messages. Importantly, different RCS implementations can talk to each other, just like email servers, or Lemmy instances.

Apple has been encouraged to enable RCS compatibility in iMessage in a loud campaign by Google, but they are obviously not very eager to do that, as their own research shows the closedness of Apple ecosystem and messaging system is a main driving factor of sales. This has been revealed in the Apple vs Epic Games case hearings