Blizzard posted an announcement that the servers would be down most of today, for unspecified purposes.
You’ll note a lack of anything like, “we’ll be installing beta patch 13 during this time” in this update. You’d assume it’s part of the whole thing, and that the servers wouldn’t come back up for a few hours, then go down again for the patch, but who really knows?
Thanks to metarox in comments for pointing to another thread, in which Vasadan breaks Bliz CM format and provides a straight answer to a question:
We’ll do our best to keep everyone updated as we go.