Boeing delivered the first updated 747-800, to Cathay Pacific. The so-called Performance Improvement Package (PIP) gives the airplane a reduced fuel usage per year of roughly 30 medium sized trucks.
For the number crunchers: the efficiency of the improved GEnx-2B engines with PIP has increased by 1.8 percent, but we frankly like the fuel truck comparison better. The Cathay 747-8 Freighter was the first jumbo jet with the update. It consists of a better engine, a software update for the Flight Management Computer and a reactivation function of the horizontal tank fuel system.
The first two can be added to existing 747-400s and -800s alike, the latter only to 747-800s.