The X5/6//7 changes have been listed on the Connect Tees Valley upcoming service changes pdf - though it lists the X7 s being withdrawn as the revised service doesn't serve the Tees Valley.
It seems the X6 will serve King Owsy Drive in Hartlepool rather than the hospital, alike the 23. This is the first time a Go North East bus has served the area.
RE: Go North East: Upcoming Service Changes v2