Monday morning is going to be a tough one for those planning an all day Steam gaming marathon, as the service is scheduled to be down for about four hours. Starting at 4 am Pacific time until 8 am Pacific, Valve says that “some” of the services will be unavailable while they perform software maintenance.
According to the announcement the affected areas will be the online portions of the service, including: the Steam community, in-game matchmaking or lobbies, downloading games content servers, and making purchases from the Steam store. Basically, anything having to do with the servers is out of the question during that time. However, any games that don’t need matchmaking, or any sort of online connections, should still remain playable while the service is down.