How to force Steam to believe it's running under SteamOS...

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 mode

There 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?
"Enable access to the Linux Desktop"?

I thought some people were saying that on the steam machines, we cannot access the linux desktop?
This has me intrigued as well since they said it wasn't just a fork of Ubuntu. I don't think having a desktop environment is quite as simple as just slapping Cinnamon, KDE, or XFCE down in your libraries.
The "enable access to the Linux desktop" bit is very interesting indeed, as it directly contradicts earlier reports. Maybe the option will be hidden and you'll have to somehow enable it?