Fujifilm GFX 50S has a Fujifilm G lens mount and currently there are 6 native lenses available for this mount.
Fujifilm GFX 50S doesn't have a sensor based image stabilization system but 1 of these lenses already comes with optical image stabilization.
Since Fujifilm GFX 50S has a Medium format sensor, it has a focal length multiplier of 0.79× so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on GFX 50S.
You may also also be interested in these:
Fujifilm GFX 50S Lenses with Image Stabilization
Fujifilm GFX 50S Lenses with Weather Sealings