Mercedes-Benz is introducing the S400, a hybrid version of its S-Class luxury sedan, in the United States. But much of the details of the upcoming S400 Hybrid are still uncertain. That includes the vehicle’s launch period. Some sources say 2009, while others say 2010. If it becomes available in 2010, it may overlap with the probable launch of the Mercedes Benz S400 Bluetec Hybrid, which was unveiled as a concept vehicle at the 2007 Frankfurt Motor Show.