If it isn't an open API it doesn't really matter. I would use gRPC (protobufs) so you get easy binding on both sides and better efficiency. If third parties wi

If it isn't an open API it doesn't really matter. I would use gRPC (protobufs) so you get easy binding on both sides and better efficiency. If third parties will need to use the API at any point I would use REST and follow Google's API design guidelines.