According to this FCC filing, Sony is working on a 4000 Series PlayStation 3.
The document could relate to a slimmer PS3, rumoured by Eurogamer to be announced at gamescom next month.
The current PS3 is the 3000 Series. The model mentioned in the filing is the CECH-4001x.
An included image appears to show the new console compared to the current model. It's a great deal smaller, seemingly.