I’m no expert on these matters (eg I know nothing about USD/USDZ formats), but OpenSubDiv is used by the dev-geometry branch, and that branch got merged into master branch before master was used to make 4.20. So it is in there, at least on windows and for use with the subdivide feature of the experimental mesh editing tools that are in 4.20. Whether it can also be accessed in other ways such as via blueprints I cannot say, since I’ve not tried that stuff and documentation is lacking. Nor do I know anything about supporting it automatically for files imported from elsewhere. I do know that a refactoring of UE4 mesh asset code was part of the dev-geometry work too, but I dont know much detail.