Grand Theft Auto IV has been pulled from Steam due to a technical issue involving the now-defunct Games for Windows Live.
Rockstar Games, the publisher behind the action-adventure game first released in 2008, says that the closure of Games for Windows Live is causing the issue. The game page remains live on Steam, but it is not currently available for sale.
In a statement, Rockstar Games explains:
Grand Theft Auto IV was originally created for the Games for Windows Live platform. With Microsoft no longer supporting Games for Windows Live, it is no longer possible to generate the additional keys needed to continue selling the current version of the game. We are looking at other options for distributing GTA IV for PC and will share more information as soon as we can.
GTA IV was released back in April 2008 for PS3 and Xbox 360. It was later ported to PC via Games for Windows Live in December 2008. Microsoft stopped supporting the platform in 2014.