Do all XBees of a certain type have the same HI 64 bit address

Are we safe in assuming that all XBees of a certain type (i.e. XB24) have the same 64 bit address HI portion (0013A200) for now and in the future? That they are only different by their LO 32 bit address?

Yes - except for the XBee XSC. This module has a serial number that matches the format of the XStream module. Also, the XTend uses a different serial number structure.