Rockstar has issued an update regarding the status of GTA IV on PC. Currently, both the base game and the standalone DLC (Episodes From Liberty City) are currently unavailable for purchase due to Games For Windows Live.
In a blog post on Steam, GTA IV will be coming back to Steam, and also on Rockstar Games Launcher, as GTA IV: Complete Edition. This includes the base game and Episodes From Liberty City.
For owners of either GTA IV or GTA: Episodes From Liberty City, you will still be upgraded to GTA IV: Complete Edition, no extra purchase necessary.
However, contrary to the name, it will also be missing a few features aside from Games For Windows Live. Multiplayer and leaderboards are gone. And the RamJam FM, Self-Actualization FM, and Vice City FM, featured in GTA: Episodes From Liberty City) will also be gone.
For those who have the physical copy of the game, or bought the game via the defunct Games for Windows Live Digital Store, there are methods to redeem GTA IV: Complete Edition detailed in the post.
No release date for GTA IV: Complete Edition has been issued for now. So the wait continues, but now we know what to expect.
Source: Steam