Xbox has officially announced that the Blackout Private Beta for Call of Duty: Black Ops 4 will begin September 14 on Xbox One.
Players can get access to the Blackout Private Beta by pre-ordering Call of Duty: Black Ops 4 on Xbox One store or at a retailer. If you already had access to the MP Beta in August, then you will have access to the Blackout beta — the same beta file on your platform will update to the Blackout beta closer to the start date.
— Xbox (@Xbox) August 20, 2018
An end date for the beta has not been announced yet.