According to Autocar, Mercedes-Benz engineer are working on a nine-speed automatic transmission.
Autocar's sources says the gearbox will be "introduced on large-capacity engines."
Motor Trend reported that the baby SLS would get a nine-speed double-clutch transmission for it's twin-turbo-V6-hybrid engine, and Automobile said that all of the next generation S-Classes, arriving in 2012, would "have hybrid powertrains and a new nine-speed automatic transmission."
Mercedes engineers thinks that "nine ratios is the maximum that is technically possible, as well as being the most that customers will be able to cope with"
Src: autocar.co.uk