According to the product page, the PS5 version will allow installation and launch of the game without downloading a significant portion of content from the network. For the boxed Xbox version, there is a requirement to download additional files.
The reason is likely related to storage capacity. PS5 discs can hold up to 100 GB of data, while Xbox Series X|S media are designed for approximately 50 GB. Because of this, larger games are easier to fully place on a PlayStation disc, while on Xbox, some data has to be downloaded separately.
The situation seems unusual, considering that Fable is associated with Xbox. Now, players on Sony's console can get a more complete physical edition. Many see this as further evidence that the boxed game market is no longer a priority for Microsoft.
Fable is set to release on February 23, 2027, on Xbox Series X|S, PC, and PS5.