https://www.gamespot.com/articles/call-of-duty-black-ops-4-blackout-beta-extended-no/1100-6461785/

Call of Duty: Black Ops 4's private Blackout beta has been underway on PS4 for the past several days, and now it's expanded to Xbox One and PC as well. Developer Treyarch continues to implement gameplay tweaks and other changes as the beta rolls on, and a new batch of adjustments have now gone live. [Update: The Blackout beta's end time has been extended until 12 PM PT / 3 PM ET / 8 PM BST. Additionally, Treyarch has updated it to now support 100 players in a single match.]

As the studio detailed on Reddit, both the Xbox One and PC Blackout betas will start off supporting 80 players, just as the PS4 version originally did. The PS4 beta, meanwhile, will maintain its recently increased 88-player cap. Treyarch says it will continue to test different player counts for the betas in order to optimize the mode before Black Ops 4's release next month.