Call of Duty: Black Ops IV is a payed game, which you need to purchase as a disc (physically) for your Xbox One/One S/Series X or digitally on the Microsoft Store, for any Xbox One/Series X|S console. Because of that, this game requires an active Xbox Live Gold subscription or Xbox Game Pass Ultimate.
Fans are disappointed as the Game Pass didn't include a single Call of Duty game. Phil Spencer, CEO of Microsoft Gaming, confirmed last year that Activision Blizzard video games will hit the Game Pass in 2024.