https://www.gamespot.com/articles/red-dead-redemption-2-beta-red-dead-online-launche/1100-6461880/

Rockstar has shared the first details regarding Red Dead Redemption 2's online mode, named simply Red Dead Online. As was the case with Grand Theft Auto V's online component, GTA Online, Red Dead Online will not launch alongside the game itself; instead, it will debut sometime in November 2018--one month after Redemption 2 itself releases--and will start as a public beta. Anyone who owns a copy of RDR2 will have free access to Red Dead Online; there's no indication the multiplayer mode will be made available separately.

"Using the gameplay of the upcoming Red Dead Redemption 2 as a foundation, Red Dead Online will be ready to be explored alone or with friends, and will also feature constant updates and adjustments to grow and evolve this experience for all players," the announcement states.