Here we go again! It's coming in now...
Shucks, I just checked 30 min. ago !!
See below for new Windows 10 build 14390 details:
Announcing Windows 10 Insider Preview Build 14390 for PC and Mobile
#NinjaCat caused double trouble today: we are also releasing Build 14388 for PC + Mobile to the Slow Ring:
Reading between the lines, releasing 14388 to slow ring two days after fast ring got it, Anniversary Update is starting to be ready and changes only cosmetics.
I have to agree Slow Ring being on 14388 - that is indicative we are nearly there. Maybe we should run a poll on final build number :-).