With the release of Forza Horizon 3 this Tuesday, September 27, Microsoft has confirmed via Polygon that the first title of the franchise will be removed from sale one month from now, on October 20. On that day, the game, as well as all of its DLC, will no longer be available for purchase.
If you own the game or buy it before that date, nothing will change, the game is yours and it will remain that way. As far as the brand new Forza Horizon 3 goes, gamers who bought the $100 Ultimate Edition can start playing the game right now, before the official release this Tuesday. You can also play the official demo until the game launches.
Forza Horizon 3 is the first game to make use of the new high dynamic range (HDR) feature of the Xbox One S.