Treyarch is hosting a special event for Call of Duty: Black Ops 3 players on PC! The event kicks off on May 30 and will last for 30 days; this event is exclusively for PC players.
Starting May 30, the Call of Duty: Black Ops 3 Multiplayer DLC Trial Back begins on PC. All PC players will be able to play all DLC multiplayer maps in Black Ops 3 for free for 30 days. Alongside, all of the DLC maps will be added into all playlists during this trial duration.
— pcdev (@pcdev) May 24, 2017
Players on PC who own the Black Ops 3 Season Pass will also get Double XP enabled on playing on all maps for the entire 30 day period. If you only own select DLC maps, you will get Double XP when you play on those maps.
SOURCE: Treyarch & PCdev