From GameWatcher: “More than one year after World War Z launched, cross-platform support is on its way in the co-op shooter’s upcoming Dronemaster Update.
Once World War Z’s Dronemaster Update hits live servers in two days’ time, crossplay will allow players to form parties and face waves of undead without being restricted by their platform.”
Source: N4G PC World War Z Gets Cross-Platform Support in Dronemaster Update