Backwards compatibility was added to the Xbox One to play Xbox 360 games in June of 2015. It was announced at the Microsoft press conference at E3 2015, with Xbox One preview members gaining access to it same day.
Emulated Xbox 360 games can take advantage of the Xbox One features, such as GameDVR, screenshots and game streaming. The games also generally run better than on original hardware, with forced v-sync and in many cases higher/more stable framerates.
Third parties have found various ways to take advantage of the technology, with some popular Xbox 360 games getting reprints and advertised as if they were native Xbox One games (although the game boxes do differ slightly and make clear that the emulator has to be downloaded).
At E3 2017 during the Microsoft press conference it was announced that original Xbox titles were going to be added to backwards compatibility.
On 10/24/2017 the first 13 original Xbox titles were made available to play. Original Xbox titles on the service do not include any updates such as working online play, but do offer a slight visual upgrade due to the increased power of the system.
Xbox One X Enhanced Xbox 360 Games
Microsoft announced that upon the Xbox One X launch a set of select Xbox 360 games would take advantage of the increased power of the system and allow the emulator to run the games at a higher resolution. These games run at 9x their original resolution, with native 720p games running at a full native 4k. The method for this is called the Heutchy Method which was named after the engineer that programmed it.
The enhanced Xbox 360 games launched with four games:
The backwards compatibility is possible through emulation. The entire Xbox 360 operating system is being emulated so technically any game can run on it.
With multi-disc games, such as Blue Dragon, Microsoft will need to repackage the games in order for them to be playable on the Xbox One.
There are some restrictions to the games that will be able to fully work using this emulation method. Any games that use an external USB device such as Rock Band or any games that use the original Kinect will not work.
Publishers will also need to give permission to Microsoft to allow their Xbox 360 games to work. Although, Microsoft plans to make every first party game playable on the Xbox One.
Removal from Service
In June 2017 Microsoft announced that Poker Smash would be removed from the backwards compatibility service. The game, even if previously downloaded was no longer able to be played or purchased. Players who purchased the game would still be able to play the game on an Xbox 360.
On June 10th, 2019 Microsoft announced the final batch of backwards compatible original Xbox, Xbox 360, and Xbox One X Enhanced games. It was announced that the backwards compatibility team would start putting their focus on backwards compatibility on Microsoft's next generation console.
On top of the final games being made backwards compatible, a number of original Xbox titles would be receiving free DLC packs in the form of title updates. The DLC added to the games were: