While the company didn't go into detail about the car, they announced it will offer an optional electrochromic glass roof dubbed Magic Sky Control. When ordered, customers can darken the top glass panel in a matter of seconds via a switch located on the overhead console.
As Mercedes explains, "The operating principle is based on the physics of a plate condenser. When the glass structure is subjected to an electrical voltage, particles in the structure position themselves so that light is able to pass through the glass. When the voltage remains switched off the particles position themselves randomly. This partially blocks the light, and the glass remains dark." Refer to attached diagram below for a pictorial description.
In addition, even when the voltage is off, the roof blocks UV and infrared rays, helping to keep the cars cabin cooler by up to 10 degrees Celsius.