What has changed are the taillights, and the front and rear bumpers. Judging by the more pronounced sideskirts, we're looking at an S-Class cabrio with the optional sport package. This is supported by the scallops in the rear bumper. These are very similar to the vented versions found on the current sport package-equipped S-Class, but they're closed up on this prototype. The faux rear diffuser has also been removed on this updated model, and the exhaust tips have been split down the middle for four outlets, rather than two.
It's more difficult to tell what has changed with the taillights. They appear to be the same size and shape. In the shot of the car driving away, we can see the lights illuminated, and the bands of light look closer together, and restricted to the top halves of the units. The changes to the front bumper are also difficult to tell due to heavier camouflage. It looks almost as though the vents on each corner aren't pulled back as far as on the current model.
The interior remains mostly unchanged, and also completely undisguised. That is except for the steering wheel, which is covered by a large piece of carpeted camouflage. It also obscures the instrument panel. So we would guess that the steering wheel has a new design, but we wonder if some new buttons and functions have been added as well. We're not sure if the instrument panel was meant to be obscured, too, but if it was, it could indicate an updated gauge cluster, perhaps with a larger screen.
Considering the minor updates involved with this refresh, we would expect the changes to show up for the next model year. We would also expect the announcement for the refresh to be made in the next few months, perhaps as soon as the upcoming Geneva or New York auto shows, depending on how far in development this vehicle is.