Microsoft made a few announcements for business customers today. The company is releasing updated media of the Windows 10 Anniversary Update (AU) for Current Branch for Business (CBB) customers. Also, the AU is coming to the VLSC (Volume Licensing Service Center) on January 26.
Because of the latter, there will be a 60-day grace period for Windows 10 version 1507, which was the original release of the OS (build 10240). You might not realize this, as all consumer PCs should have been upgraded to at least version 1511 by now, but Microsoft still releases 1507 cumulative updates every month. The most recent was on January 10.
As of March 26, version 1507 of Windows 10 will no longer receive those updates, as only the two most recent feature updates of the OS are supported. In other words, once the upcoming Creators Update hits VLSC (probably late 2017), there will be 60 days before support for 1511 ends.
Again, these changes shouldn't affect anyone that's on the Current Branch, as those users should have the latest feature updates. According to Microsoft, this should only apply to CBB customers.
Source: Microsoft TechNet
Editor's note: This article was updated after publishing to include a link to Microsoft's announcement.