It was reported a few days ago that Xbox One X titles that feature 4K assets will need to download the packages in order to fully utilize the enhanced visuals. It turns out this may not always be the case.
Xbox Boss Phil Spencer was recently asked on Twitter if 4K assets will have to be downloaded even if someone purchases the physical copy of the game. According to Spencer, that decision is “up to the developer”. He mentioned that you’ll have to download the assets for already released titles (like Forza Horizon 3 which is getting an Xbox One X update), but as for new games, it will depend on whether or not the developers can fit all of the content on the disc.
For games already shipped you should expect DL if needed, for new games it's up to developer, they can't put on disc or dl.
— Phil Spencer (@XboxP3) June 29, 2017
One reason why some folks want to avoid downloading the assets is due to the massive file-size that accompanies them. For instance, it’s been reported that the upcoming Forza Motorsport 7 will have a massive download size of 100GB. Obviously not every Xbox One X-enhanced title will be that large, but more complex games like Forza are a no-brainer in this regard. The Xbox One uses Blu-Ray discs, which have a maximum size of 50GB. So, games like Forza are most certainly going to need to download additional assets that cannot fit on the disc.