They're calling it Red Dead Online and a beta for it is planned to begin in November 2018 for everyone that owns the game on either the PlayStation 4 or Xbox One.
Red Dead Online is an evolution of the classic multiplayer experience in the original Red Dead Redemption, blending narrative with competitive and cooperative gameplay in fun new ways. 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.
Rockstar says that they "look forward to working with (their) amazing and dedicated community" in order to share ideas and fix "teething problems." Rockstar continues on to say that they want to have Red Dead Online become "something really fun and innovative."
Red Dead Redemption 2 will be released on October 26, 2018.
I just hope they fix the: loading times for everything, lobbies for everything, waiting for everything, no party systems, hackers... which were all pretty much a step down in GTA O from the original RDR multiplayer