Rocket League developer Psyonix has revealed that PC and Xbox One players will now be able to join and compete against one another in online play.
Both public and private matches will now allow you to find players from a pool that includes players from both platforms, unless you turn the feature off in the options menu.
This feature will go live today at 3pm PT/ 6pm ET/ 10pm UTC.
https://www.vg247.com/2016/05/24/rocket-league-pc-xbox-one-cross-platform-multiplayer-coming-today/