Although Windows XP official support died years ago, it has still had the support from many programs and features to this day.
But sadly, Steam’s last day of XP support has finally arrived. Starting tomorrow, January 1, 2019, Steam will no longer work on Windows XP. If you want to run your games, or use any Steam feature at all for that matter, you’ll need to update to a newer version of Windows if you’re still running XP.
In addition, Valve states in their support article that future versions of Steam will require Windows feature and security updates that are only present in Windows 7 and above.
What’s sad to see is that Steam will not implement any sort of lite launcher or client that allows XP users to still play their games without a full OS upgrade.