The original Dark Souls is now available on Xbox One backward compatibility. If you own a digital version, head to the My Games & Apps section to download it. Alternatively, pop in the original Xbox 360 disc and you'll be prompted to give it a download. You'll need 4.6GB of HDD space to install it.
The game's arrival on Xbox One backward compatibility comes ahead of Dark Souls 3's release next month. As previously announced, anybody who pre-orders a digital Xbox One copy of Dark Souls 3 will also receive a copy of the original for free.
Alan Wake, Assassin's Creed, Castlevania: Symphony of the Night, Pac-Man, Dark Void and GRID 2 were all added to Xbox One backward compatibility earlier this month. [UPDATE: Tekken Tag Tournament 2 is now available, too.]
Dates for previously announced backward compatibility titles Red Dead Redemption, BioShock Infinite and Call of Duty: Black Ops, however, have yet to be announced.
Source: Xbox One (thanks @ChrisLittle1983)