Looks like our earlier reporting was slightly ahead of things as build 10586.63 is now live for those on the Insider program and in the Fast Ring. At least for some users.
No word just yet from Microsoft on what is new, but the update is confirmed as going out to our Lumia 950 XL. However, our Lumia 950 on AT&T is not seeing the update for whatever reason and many others are not seeing the update either. Microsoft is conspicuously quiet about this update with no announcement or information.
We'll add to this article as more information becomes available.