It’s finally happened. Rocket League has joined the PS4 Cross Play beta which means you can now compete with those playing on Xbox One and Switch, as well as PC. To take part in the cross play shenanigans you need to go Options, Gameplay, and then check the cross-platform play button. You can’t create cross-platform parties yet but an update will be released to allow that eventually. However, you can create private matches with people on other platforms.
All online match types will be available so if you want casual, competitive, or the extra modes then feel free to do so. Psyonix has thanked the fans and players for making this possible.
Source: PS Blog