Updated 12/31/18, 1:45 p.m. ET: We've updated the headline and date of this story to give any gamers still running Microsoft's older operating systems a heads-up that the Steam client will stop running on their machines when the clock ticks over to 2019. Luckily, you can get a copy of a newer Microsoft OS for free or cheap.
Despite Microsoft having already checked Windows XP and Windows Vista into the retirement home, many consumers still use one of the two operating systems even to this present day. However, you simply can’t stop evolution, and most software developers are already starting to phase out support for the moribund operating systems. Now it seems Valve is the latest company to abandon the time-worn Windows of old.
Valve announced that starting January 1, 2019 the Steam client will no longer work on PCs running the Windows XP or Windows Vista operating systems, giving Steam users have no other choice but to update to a more recent version of Windows. Most already have: According to Valve's latest Steam Hardware Survey, less than 1% of the user base is still on Windows XP, and Windows Vista didn’t even appear in the results.
That means the impact of Valve’s decision shouldn't be significant, but as a sign of good faith, the company is giving affected users what is left of the year to make the transition. In the meantime, Windows XP and Windows Vista users can continue to launch their games during this grace period. They won’t be able to access new Steam features, such as the Discord-like that's currently in open beta, though. update
Based on Valve’s explanation, the latest features in the Steam client depend on an embedded version of Google’s Chrome browser. Google pulled the plug on support for Windows Vista back in 2012 and did the same for Windows XP two years later. Valve also confirmed that future versions of its Steam client will rely on features and security updates that only Windows 7 or newer operating systems can offer.
Microsoft plans to end support for Windows 7 in 2020, which is a little over one year and seven months from now. So it makes sense for people to finally upgrade to the latest Windows 10 once and for all, since that's the version of Windows that Microsoft plans to support going forward.