With backwards compatibility now available for the Xbox One, the hit Dungeon Siege III that is offered for free on Xbox 360 is now free as well for the Xbox One.
Unfortunately, you can’t get Dungeon Siege III right on the Xbox One’s Games with Gold page. To get Dungeon Siege III loaded on your Xbox One, go to the Dungeon Siege III game page on Dungeon Siege 3 – Xbox One Game with Gold and queue it from there. Once you do, the game should appear on the Ready to Install section under the My Games section.
Please note that only Xbox Live Gold subscribers can get the Dungeon Siege III for free.