As the Atlas press release says, GSS will get Atlas' first THREE 747-8F. What is NOT said but long been told to the flight crews is that the 3 747-400F's currently flown by GSS will return to N-registration and the Atlas certificate. Still a net gain of 3 airframes for the aircrew at Atlas.
So it appears that GSS will not shrink or grow, just swap -400F for -8F.
ACG