Andrew Schnickel explains what this means:
“One of the major implications of this work is that the XDK upgrades now allow us to support Xbox One X features such as increased resolution and visual enhancements. We can also use platform advancements such as the ‘social manager’, which simplifies a lot of our code around friends and presence management. And foundationally, this update opens the possibility for other things we’d like to explore like custom game session browsing, Xbox Arena or Mixer support.”
According to Greg, updating all eight game engines includes fully retiling textures, recompiling shaders, etc. which is why MCC will eventually require a sizable re-download when it launches. It’ll definitely be worth it.
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"This is by no means everything that’s been done so far but with this great foundational refresh complete, the team has been able to start on a number of other big ticket items including general bug fixing, visual enhancements for Xbox One X, and more."