Xbox Live is about to change how the gamertag works. The service now allows you to change your nickname in the system to whatever you want (within the rules), but at the same time you will receive a numerical designation. This applies to Discord and Battle.net.
Right now you
"The Xbox One console and mobile app will soon be updated to show your new gamertag," reads
However, it should be borne in mind that after changing the tag, your previous nickname will become available to other users.
Source: 3dnews.ru