It’s been announced that World War Z crossplay for Xbox One and PC players will start today, March 23. This has been shared on the official Twitter account. As you can see, PS4 players are not included, so this is not the full cross-platform play everyone has wanted.
Saber Interactive's World War Z can be played on all 3 platforms, but only players on Xbox One and PC will be able to matchmake and join forces in the game. Still, there’s hope for PS4 players because it’s also said that crossplay with PS4 will arrive in the future.