They're merely moving you from dedicated Xbox One beta servers to the same servers currently being used for Stress testing next week. (Moving you from one beta server to a different beta server). They've most likely got a GPP4 build (in line with 1.4 Stress Test) going through Microsoft Certification as we speak.
I very much doubt anything will change with regards to your save, your client will simply connect to a different server than it does currently. You're still not moving to the live servers until October 6th.
Does anyone know how this affects exploration data? Just losing my first finders fee amounts to about 20mil in progress toward elite rank (don't care as much about creds)
I already lost about 5 mil in their unannounced build update...