Though tokens for the Gears of War 4 beta on Xbox One were due to go out earlier this week, Microsoft encountered some issues getting them out to those set to receive them. The Coalition, current developer of the Gears of War franchise, says that due to the issue, codes were not distributed as originally intended.
From The Coalition (via GameZone):
Microsoft Operations had an issue this morning with their code drop and unfortunately the codes will not be distributed in chronological order as originally messaged. We will be doing another code drop this evening to help address some of the issues. As noted before, codes will be going out in waves as we ramp up our servers through the beta.
Code distribution should be complete by the evening of Thursday, April 21. The beta opens to all Xbox Live Gold members on April 25. Gears of War 4 launches to the public on October 11.