The sun may still be rising in the United States, but other parts of the world are already struggling with the latest cumulative update for Windows 10 version 1511 (aka build 10586, Threshold 2, or the Fall Update).
The official Microsoft explanation for this new patch, known as KB 3116908, simply says:
This update includes improvements to enhance the functionality of Windows 10 Version 1511.
Of course, if your PC is still stuck on the July 29 RTM version of Windows 10 -- build 10240 -- you aren't getting any recent cumulative updates.
I've seen complaints that people trying to install CU 4 are triggering an error 0x80070570, which is a general Windows Update error message. There's a complex five-step process to work around the error, posted by Microsoft as KB 910359, but it doesn't always work. I've also seen several independent reports that the cumulative update knocked out Wi-Fi on various PCs, a problem that could only be fixed with a system restore.
Poster H_He_Metals on Reddit complains that after installing the patch, "Chrome crashed a few times, MS Edge crashed once, Desktop Window Manager caused the video driver to crash, My Murmur server even crashed, and the up arrow on the keyboard refused to work."
Under normal circumstances I would attribute those kinds of problems to an unfortunate accident, but the poster insists that after he uninstalled the patch, everything worked properly.
Here's how to check your PC to see if you're on the latest upgrade trail. Start with the About Windows dialog (see screenshot), which you can get to by typing "winver" in the Cortana search box and pressing Enter.
If you see "Version 10.0 (Build 10240)" on the second line, you're still running the original July 29 RTM version of Windows 10. There are many reasons why you might still be stuck on the original Win10. Perhaps the installer for version 1511 has repeatedly failed to run. Build 1511 also won't install if you upgraded from Win7 or 8.1 to Win10 fewer than 30 days previously and there's still a windows.old folder on your system. (If you aren't going to roll back to Win7 or 8.1, using an admin account, right-click on your c: drive and choose Properties > Disk Cleanup > Clean up system files.)
If you see "Version 1511 (OS Build 10586)," as in the screenshot, you have the first version of Threshold 2, which shipped on Nov. 12. Variously known as the Win10 Fall Update, November Update, Threshold 2, and other less-printable epithets, it's the version of Windows 10 that (in my opinion) should've been called Win 10.1 or Win10 SP1 or Win10 SU1.
Since those halcyon days, a mere three weeks ago, Windows 10 version 1511 has undergone several major changes. Cumulative updates change the OS build number, and you can judge your PC's progress at installing those updates by looking at the build number.
Build 10586.3 is what you get after you apply Cumulative Update 1 (KB 3105211) to build 10586. That's the only version 1511 cumulative update that has any sort of description. It references six security bulletins and two security advisories, and the patch apparently encompasses all of them. The 64-bit upgrade file runs about 50MB.
Build 10586.11 includes CU 2 (KB 3118754), released Nov. 18, and according to the Microsoft Update Catalog it runs 157MB. (Yes, it's true, the Microsoft Update Catalog only opens properly with Internet Explorer.) There's no description of what the patch does. In the Software Update Services list, this one's listed as an Update, not a Cumulative Update.
Build 10586.14 appears after you apply CU 3 (KB 3120677), released Nov. 24. This is the patch that was released shortly after Microsoft reversed its earlier decision and started making build 1511 available for direct download. The x64 file runs about 163MB. This is the KB article that, infamously, links to KB 3121244, which describes how Microsoft had accidentally changed four privacy settings.
Now, Build 10586.17 signifies that you've applied CU 4 (KB 3116908), released Dec. 2. At this point, we know nothing about the patch except that the x64 file runs 230MB -- a hefty bump up from CU 3.
Four cumulative updates in three weeks, 230MB of changes with essentially no documentation. Oh boy.
In addition, there have been several other updates to build 1511 whose exact functions have not been well documented. On Nov. 18 Microsoft also released KB 3116278, described as an "Out-of-box experience update." On the same day, Microsoft released KB 3116903 as a "Compatibility update for upgrading to Windows 10," with no further explanation. On Nov. 11 we got KB 3106246, a separately identified update for the DVD Player. On Nov. 10 there was a security patch, KB 3103688, which patched the Flash Player in IE11 and Edge.
Remarkably, though, with a few outlying exceptions, there seem to have been few problems with the patches -- other than installation problems. That could change in a heartbeat, but it's a positive sign.