Grand Theft Auto IV: Complete Edition replaced today both Grand Theft Auto IV and Grand Theft Auto: Episodes from Libery City on Steam.
The new version of game no longer support Games For Windows Live, Multiplayer Mode and Leaderboards. Some radio stations are also temporarily unavailable (RamJam FM, Self-Actualization FM, Vice City FM). The Steam version of game now includes Steam Achievements.
On March 24, Grand Theft Auto IV: Complete Edition will be available again for purchase on Steam and Rockstar Games Launcher.
Source: Rockstar Games website.