Build feed shows .12 was made 11 days ago so I believe it will be out before the end of the week or the 8th for patch Tuesday. But then again they can push it out whenever they feel that its ready and stable.
The download of the ISO of windows 10 v1803 from the microsoft page is only available if it is accessed from a device that does not have windows installed, example android, otherwise appear in options only the tools of update and media creation tool Microsoft and its Customer Service User ..
I tried to update version 1803 on my Acer Iconia W510 tablet with keyboard (which already have version 1709) and here's it says: Sighs.....
It's available for WIndows users when MSFT opens it, for now the techbench unlocked scripts or websites can offer the links.
My Hyper-V install went very well from b16299.402 to b17034.1 off a x64 DVD & DL .ISO by MS Media Creation Tool. The Hyper-V is installed on my MS Test partition w/ b17655.1 OS. The install took 25 minutes to hit the desktop. Lots of new lock screen/spotlight images... nice. Glad I tested it 1st on Hyper-V before installing this one on the Main Rig. Like to be a bit cautious on new W10 feature updates.
I have 17134.5 as well and wont be paving over it until a publicly available CU for RS4 is available.