From The Manufacturer/Wikipedia/People Smarter Than Us:
The successor of the STEYR PISTOL S now available in the new version: STEYR PISTOL S-A1
An overview of the advantage to the old model:
Ergonomical improved grip with picatinny rail
Conversion kit for 9×19, .40S&W
Low profile like on the series M-A1 therefore you have nearly no muzzle climb
Increase of function safety in the calibre 9×19 thanks to a new clearance
Possibility to mount a sling on the grip