Xbox has confirmed exactly how Smart Delivery will work across your the Xbox platform. The most important thing is that they have confirmed that it will work for both physical and digital titles.
They’ve given three examples to how this could work. The first is that if you own Gears 5 (or any other Smart Delivery game) on Xbox One, you’ll be able to play it day one on your Xbox Series X with the improvements for free.
Another example is if you decide to purchase Halo Infinite (or play it on Game Pass) on Xbox Series X, but still keep your Xbox One, you’ll be able to play the game on both consoles and they’ll both recognise which version to serve you.
The third example relates to third-party games such as Cyberpunk 2077, which you’ll be able to pick up on Xbox One come September then continue on your Xbox Series X when that comes out later this yaer.