>>64501315 (OP)
the X is a short slide on a 12 round frame instead of a 10 round frame.
That's obviously a 12 round frame and the slide extends past the dust cover so it's a longer slide. Its an XL.
note that its the updated version that has the sights cut separate from the optics cut. The first few production runs of the XL had the sights as part of the optic cut so you lose them when you put a red dot.
Not that it matters on a p365. With the XL slide and the FCU you basically can just have everything from a super micro to the FUZE or xmacro or whatever the fuck the newest versions are, just by buying a 50 dollar chunk of plastic frame.