The service can be enabled for up to five Steam accounts to share a single collection of games across as many as 10 different computers. During the beta that Valve had been running until now, the limit had been 10 users. Under the Family Sharing program, Steam maintains game saves in the Steam Cloud and tracks achievements for each account.
Valve announced Steam Family Sharing and launched a limited beta last September, and last month, the company increased security by adding two-factor authentication. According to Valve’s Family Sharing FAQ, individuals must be online in order to play games in libraries that are shared with them. And whether there are one or 10 Steam users authorized to share a library, multiple people can’t be playing at the same time — only the account holder, the person whose library is being shared, maintains unlimited access to their games at all times.