According to the first information, the upcoming 16C Galibier will be powered by the same 8.0 liter W16 unit that equips the Veyron.
Compared to the coupé, the sedan will have two turbochargers instead of the four of the Veyron, and an eight-speed automatic dual clutch transmission instead of the seven-speed DSG.
(Source: Bugatti via Autoblog)