After Activision and Treyarch have announced the starting date for the Call of Duty: Black Ops 4 Blackout Beta on the PS4, the dates for Xbox One and PC followed.

In a short teaser, Treyarch and Activision recently revealed the starting date of the PS4 Private Beta for Call of Duty: Black Ops 4’s in-house Battle Royale mode. The Blackout Beta starts on September 10, 2018, at 7:00 PM. As it has now been confirmed, Xbox One and PC will follow just a few days later.
Call of Duty: Black Ops 4 Blackout Beta on Xbox One
When does it start? There will be a Private Beta for the new Battle Royale mode of Black Ops 4 on Xbox One. The test phase starts on September 14 at 7:00 PM. When the Private Beta ends is still unknown.
How do I get in? The Private Beta is again reserved for pre-order customers. There is currently no information about an open beta phase for the Blackout mode on Xbox One.
Call of Duty: Black Ops 4 Blackout Beta on PC
On PC, there will be both a Private Beta and an Open Beta for the in-house Battle Royale mode of Black Ops 4.
Call of Duty: Black Ops 4 Blackout Private Beta
When does it start? The Private Beta starts on September 14 at 7:00 PM. However, the Private Beta will transition into an Open Beta just one day later.
How do I get in? Access is only granted as a pre-order of any digital version of Call of Duty: Black Ops 4.
Call of Duty: Black Ops 4 Blackout Open Beta
When does it start? The Open Beta for the Blackout mode on PC starts on September 15 at 7:00 PM. When the Open Beta ends is still unknown.

How do I get in? Anyone with a Battle.net account can participate.
The game modes of the Call of Duty: Black Ops 4 Blackout Beta
This is how it will be played: According to the teaser, it will be possible to compete in the modes Solos, Duos, and Quads accordingly alone, in pairs or in a four-man team. The maximum number of players and the exact contents of the Blackout Beta are still unknown.
By the way: If you have already participated in the Private or Open Beta of the traditional multiplayer part of Black Ops 4 and are now considering checking out the Blackout Beta – do not delete the previous beta client from your hard drive. This could save you a lot of time in the Call of Duty: Black Ops 4 Blackout Beta.