The Steam digital distribution service from Valve will stop with the New year support the operating systems Windows XP and Windows Vista. This is stated in the official report in Steam support.
From 1 January 2019, the Steam client will not run on these versions of Windows. As explained by the developers to be able to run games or other products purchased in Steam, users will need to update its operating system to a later version of Windows.
The fact that fresh features in Steam are relying on the embedded version of Google Chrome, which does not work on older versions of Windows. Moreover, for future versions will require Steam features and security updates that are only available in Windows 7 and above.
Until the end of 2018 Steam will work and run games on Windows XP and Windows Vista, however, other features of Steam will be somewhat limited. For example, a new Steam chat will be unavailable.