https://www.gamespot.com/articles/heres-why-red-dead-redemption-2s-online-mode-relea/1100-6461897/

Red Dead Online, the new "online connected experience" for Red Dead Redemption 2 will not be available at launch. Players will have to wait until sometime in November to try it out, when it debuts in the form of a beta open to all owners of the base game on PS4 and Xbox One.

But why? Design director Imran Sarwar said in a new interview that Rockstar sees the single-player and the multiplayer elements as "separate products." Each will "grow and evolve independently of each other," he told IGN.