As usual it's a joint "marketing" deal in this case:
"As for Microsoft’s Xbox Series X, Sweeney isn’t saying the new Xbox won’t be able to achieve something similar; both are using custom SSDs that promise blazing speeds. But he says Epic’s strong relationship with Sony means the company is working more closely with the PlayStation creator than it does with Microsoft on this specific area." link
This is Sweeney bog standard copy/paste answer every time a new tech is announced alongside & HW manufacturer (usually Nvidia).
Tim literally said on the live stream that both Next Gen consoles & high end PCs would run Nanite as seen in today's demo.
Yeah they specifically refrained from saying Xbox when asked about other platforms. In fact, I only counted Tim saying 'Xbox' twice, but it was in reference to the Epic Login & linking platforms.
Tommy McClain