Yes, this has plagued me this whole week, and I have been hammering the internet looking for a fix. None of the computers on my DC have started it yet, but I talked to an admin with 500 machines on his DC and dozens of them had started the download. I have heard anywhere from 3 gb to 6.5gb in size once downloaded.
My own network is far from complete, mostly remote (135 computers) and I have not spent the money yet to hire an administrator to complete the domain network and manage all those computers. I get by just fine usually without the added costs, although I have slowly worked toward building the infrastructure to support a full AD network. I already work 50-60 hours a week and I have a hundred other projects on my plate that take precedence over something that will save me some time once in a while. I could come up with excuses for not having a full MS network all day long, and while they are very legitimate, it doesn't matter. If I were a home user on a Wi-Fi hotspot on my cell phone browsing facebook and checking my email and found I used 3 gigs of bandwidth at a cost of $50-100 in overages, I would be ready to sue. In my case, I have the potential for this to happen with ~60 employees, and on top of this I have had to limit internet bandwidth and spend several hours troubleshooting why 14 of my remote locations are suddenly saturated to 100% and my employees can't access our ERP software effectively. Most of my remote locations are on T-1's with 1.5 mbps.. When 4 computers suddenly start downloading a 3 gb file, it doesn't leave any room for doing business.
The thing that is really unacceptable here is there is NO WAY to stop it once it starts, short of turning off windows update completely (stopping the wuauserv service). I have removed any and all KBs associated with the update, nothing. The download message is in the tray with the update icon, but you can't click it and if you open windows update, it isn't there to stop, hide, or modify. I have also modified the registry entry that was added that changes group policy on the computer to enable the new "don't install a new OS" option. The download still restarts after 10-20 minutes and doesn't stop until it is finished.
I have heard rumors that MS has throttled the download so it doesn't eat up all your bandwidth, and so far I am seeing that in my remote locations (half the max bandwidth is eaten up, not 100%).
Supposedly NOTHING for windows 10 should happen if you are connected to a domain controller, have volume licensing, or run your own WSUS server. I have verified that when connected to a domain controller it will still download the file. I can't speak for the other conditions.
As much as I wouldn't trust some random .exe that is supposed to fix this, in reality that is exactly what I need: a simple script or executive file I can send to my laptop users and remote desktop users to run that kills this download if in progress, and if not started yet, removes any and all Windows 10 update notices, downloads, updates, or reservations.
At this point the only viable solution I have available is to limit internet bandwidth, maybe edit group policy on individual computers to slow BITS down during business hours, and just ride it out for the next sever weeks during the peak of my busy sales season. Hopefully some lawsuits will get started by people who have been monetarily affected and MS will release a fix.exe program to stop it from getting worse. I think I have aged another year this week with the stress of dealing with this BS.