https://www.gamespot.com/articles/call-of-duty-black-ops-4-all-multiplayer-maps-at-l/1100-6462449/

Call of Duty: Black Ops 4 launches with 14 multiplayer maps. There's already a 15th map scheduled for November as a post-launch expansion, but it will be free for all players.

Right now, players have access to Arsenal, Contraband, Firing Range, Frequency, Gridlock, Hacienda, Icebreaker, Jungle, Militia, Morocco, Payload, Seaside, Slums, and Summit. Four of the maps--Firing Range, Jungle, Slums, and Summit--are all from previous Black Ops games, but with a visual upgrade. In November, the Call of Duty classic Nuketown, also remastered with upgraded visuals, will become available. Treyarch hasn't announced how map updates after Nuketown will work, but they'll probably be a part of paid DLC expansions.