The 57th and 58th floors are in fact two-storey loft units. I believe it's the highest section of the building with two-storey units - the rest are in the lower floors, primarily on the 5th, 7th, 9th and 11th floors.
From the floor plans I've seen for the 57th/58th floor units, they look amazing with 1,000 sq.ft - 2,000 sq.ft. units and mezzanines and interior balconies. Actually, you can even see a cut-away portion of the cement floor in the photo above on the left side of the building where floor 58 is, which will likely become a two-storey wall of windows to someone's living room on floor 57.