https://wccftech.com/rocket-league-ps4-crossplay-launch/

Back in Fall of 2018, Sony relented and let the PS4 version of Fortnite join the crossplay party. It was promised more PS4 games would getting crossplay soon, and then…nothing happened. Thankfully, after months of radio silence, Sony is opening up again and letting Rocket League join the PS4 Crossplay Beta program. That means, as of today, PS4 owners can engage in some car soccer with players from all other platforms. Rocket League’s cross-platform party system is also coming soon.

Rocket League developer Psynoix had the following to say about true crossplay finally coming to their game…