https://www.theverge.com/2017/9/18/16327964/xbox-playstation-4-cross-platform-play-fortnite

Microsoft first announced support for cross-platform play at E3 last year, but Sony has been hesitant to enable it. Eurogamer reports that Reddit users have noticed that Epic’s co-op survival game, Fortnite, has been quietly updated to support cross-platform play between Xbox One and PS4 players. It’s not clear if Microsoft and Sony are both supporting this, or whether it’s a temporary glitch. The Verge has reached out to both Sony and Epic Games, to confirm whether this has been officially enabled.

Earlier this year, Sony refused to enable cross-platform play for both Rocket League and Minecraft, despite Microsoft and Nintendo both supporting it across Xbox One, PC, and Switch. Rocket League developer Psyonix previously said the game would support PS4 cross-platform play in “less than an hour all over the world” if Sony removed its blocks.