If you have been one of the first users to try out SteamOS, you should know that currently SteamOS has official support for Intel and NVIDIA hardware only. Gamers with AMD products in their machines will have trouble finding the right driver that will work with SteamOS.
Users can try to install older version of AMD Catalyst drivers, but the recent versions of the the Catalyst driver is not working properly on SteamOS. The list of supported operating systems for AMD Catalyst 13.12 driver include Red Hat Enterprise Linux 6.3 and 6.4, Novell SUSE Enterprise Linux 11 SP3, openSUSE Linux 11.4 and 12.1, and Ubuntu 12.04.2 and 13.04. It also lacks support for Linux Kernel 3.12.
Valve has released a statement apologizing for the issue even though valve had officially announced support for NVIDIA and Intel based systems only:
There are outstanding interaction problems between recent Catalyst drivers and SteamOS; AMD is aware of the issues and investigating. We apologize for the inconvenience and hope to get this resolved soon.
People who have tested AMD graphics card with SteamOS have reported that the machine boots have as usual and functions normally. However, the system specifications shows 0.0 video memory, which means users cannot play any games, ironically that is what the OS has been primarily developed for.
Looks like, people with AMD hardware will have to wait till the issue is fixed. We really hope Valve can bring in official AMD support for SteamOS as soon as possible.
Source: Steam Community