The current Steamclient.dll includes the following entry for command line parameters :"-steamos : forces Steam to believe it is running under SteamOS"you need:- the latest Beta client (opt-in via the preferences menu in steam)- run Steam.exe with command line parameter -steamos- run big picture modeThere is not that much difference from the normal Big Picture Mode...More interesting is the wording of the command line parameter description. It seems like Steam (as in the Big Picture Mode) is just a part of SteamOS and there might be more to it than just being a simple Steam client?