It was really only a matter of time before the Brabus Rocket 900 Cabrio became the world's fastest four-seat convertible. Brabus already produced the world's fastest four-dour droptop in the form of the 850-hp 6.0 Biturbo Cabrio, and released an 888-hp Rocket 900 hardtop based on the Mercedes-Benz S 65 at the Dubai Motor Show in late 2015. The new Brabus Rocket 900 Cabrio will cost around US$400,000, produces similar power and torque to the Rocket 900, and has the same top speed of 217 mph (350 km/h). It will be shown for the first time at Frankfurt next week.
The Brabus Rocket 900 Cabrio pretty much follows the same formula already employed with the Rocket 900 – it's all naked carbon reshaping and sculpting of the aerodynamics, a completely reworked version of the 6.0-liter V12 to 6.3 liters and a boost of peak horsepower from the standard car's 621 hp, all the way to 888 hp. That's the original non-modified Mercedes base car below.

Peak torque has been increased by a similar margin from 1,000 Nm to 1500 Nm (738 to 1,106 lb-ft), though Brabus limits the torque to 1,200 Nm (885 lb-ft) electronically, no doubt thinking about the longevity of the drivetrain, the modified seven-speed auto and the Continental 295/30 ZR 21 high-performance tires.

The car comes "standard" with Brabus Monoblock Platinum Edition 21-inch forged wheels, though 22-inch wheels are available as an option.

Perhaps the trickiest part of the entire car is Brabus' patented sport exhaust system with electronically-controlled exhaust flaps that can be transformed from citizen sound levels to ridiculously loud at the touch of a button on the steering wheel.
All the parts used in constructing the new four-seat supercar can be fitted directly to a standard Mercedes, including the 400 km/h (249 mph) Brabus speedometer.
Source: Brabus