A month ago, Microsoft announced that Windows 10 Version 1511 has reached the end of support and would no longer receive security or quality updates. Still, the "November Update" received a new cumulative update two weeks ago, showing that Microsoft could well push back support for this older version of Windows 10.
As it turns out, Microsoft confirmed today that it's extending support for Windows 10 version 1511 until April 2018, but it's only doing so for users of Windows 10 Enterprise and Windows 10 Education. The reason for the extended support is to help early enterprise and education customers who are still finishing their transition to Windows as a Service. Microsoft's Michael Niehaus notes the issue on the TechNet blog, mentioning that enterprise and education users with version 1511 will have access to Patch Tuesday updates until April 2018:
We will be providing a supplemental servicing package for Windows 10, version 1511 for an additional six months, until April 2018, providing updates to address critical and important security issues that arise during that time. These updates will be available to anyone using Windows 10 Enterprise, version 1511 or Windows 10 Education, version 1511. Updates will be offered via all normal channels, including Windows Update, WSUS, Configuration Manager, and the Windows Update catalog.
Again, this change only impacts the education and enterprise SKUs of Windows 10 version 1511. Customers running Windows 10 Pro or Windows 10 Home version 1511 should still immediately update to the latest version of Windows 10 in order to receive the latest and greatest features as well as security and other quality updates.