As noted by users over at the Steam forums, Grand Theft Auto: Vice City was removed from Steam around October 27th. This is just a few days before the 10th birthday of Vice City which was on October 29th. Upon further inspection, Vice City was also removed from a number of other digital download places such as the Mac App Store, Amazon, Green Man Gaming and even Rockstar's own storefront. GameStop had it for a few extra days but it too has removed Vice City.

Rockstar has not yet released a statement as to why it was removed. Some are suggesting it's a songs rights issue, however physical versions of the game are still available, even via the Rockstar Warehouse. Another theory is the game is getting updated due to the 10th anniversary mobile port that is releasing this later this fall, however this is unlikely and would not explain the sudden removal as the game could easily be updated.

If you currently own Vice City (and was claimed on your account) on any of the services, you should still have access to the game as normal. However, if you had purchased the game as a gift and had yet to send it to someone to claim, you no longer have access to it and can no longer send it to someone. Same applies if you had purchased the GTA Complete pack as a gift and hadn't sent it to someone or the person had yet to claim it, they will no longer get Vice City from the pack. (See update below) If you are in this situation, contact support and let us know their response.

EDIT: Fellow Russian fansite Grand Theft AG passed along this information

Last week we’ve held the sweepstakes with GTA Complete Pack steam gift as prize and there was some concern regarding Vice City being excluded from the store. Fortunately, our winner reported he had no problem with getting the game from the pack, which he received and activated on November 3. So it is still possible to get digital copy of Vice City on Steam from GTA Complete Pack if the package was purchased and stored at inventory before game’s disappearance.

So it seems if you had a giftable copy of the GTA Complete pack and proceed to gift it, it will include Vice City dispite the pack not listing as such in it's description.