Production of the Steinberger GM4 began in 1988 and ended in 2001. The Steinberger GM4S was the standard GM4 model - with passive pickups and the S-Trem bridge. Optional extras for the GM4 model were the Trans-Trem (GM4T) and active pickups (GM4SA). You could also have combinations - for example the GM4A has both Trans-Trem and active pickups. Pickups were an EMG 85 humbucker at the bridge and two EMG SA single coils.
Most of the early GM4 guitars were had bound flat tops: either black or red with white binding or white with black binding. Although some custom finish models were also made. Steinberger used bodies supplied by various OEM manufacturers (including Unico, Roscoe and Guitabec). When Gibson took over Steinberger the production of bodies moved in house. These Gibson made bodies did not have binding and had more of a curved edge on the top and a more sculpted heel- some featured figured maple tops with transparent finishes. Gibson also used alder (presumably for solid finished bodies). There were a wider range of finishes on the Gibson produced models including: Natural oil, Clear, Clear Red, Clear Blue, Clear Green, Clear Purple, Clear Amber, Cherry Burst, Honey Burst, Fire Burst, and of course Black or White
Source: Steinberger world.