Thats right its 2XP/2X Merits/2X Tiers + Free MP DLC This Weekend, for the lovely people Treyarch.
From there Reddit page
MP DLC Free Access Weekend + 2XP/2X Merits/2X Tiers Starts Tomorrow
Starting at 5 pm GMT tomorrow through 5 pm GMT Monday, March 18, all Black Ops 4 players get free access to all four current Black Ops Pass Multiplayer maps: Elevation, Madagascar, Casino, and Lockup.
e’re also turning on 2XP in Multiplayer, 2XP in Zombies, 2X Merits in Blackout, and 2X Tier Progression for players on all platforms this weekend. Grab your friends, jump in, and rank up.