Microsoft issued a reminder to organizations that it will be ending product support next month for .NET Framework versions 4, 4.5 and 4.5.1.
Starting on Jan. 12, 2016, those versions of the product will become unsupported software. As a consequence, they won't get future updates from Microsoft, including security patches. The lack of patch support could pose risks for organizations continuing to run the software.
The January deadline maybe will come as a surprise for some organizations because Microsoft accelerated its traditional product support deadlines for those .NET Framework versions. Previously, the .NET Framework product lifecycles had been associated with underlying Windows product lifecycles. Instead, Microsoft switched to a more arbitrary January deadline for versions 4, 4.5 and 4.5.1. The policy change was announced in August of last year.
Microsoft made the change in order to "invest more resources towards improvements of the .NET Framework," per its announcement.
Microsoft is claiming that organizations can simply install .NET 4.5.2 or higher versions and most things will work. The most recent version of the product is .NET Framework 4.6.1.
The newer versions of the .NET Framework will install as "in-place" upgrades, which means that older versions don't have to be uninstalled first. The .NET Framework versions from 4.5.2 and newer will support applications that used the older .NET Framework versions in most cases, Microsoft has indicated. However, it's still up to organizations to test their applications first and see if they'll be compatible.
Microsoft's announcement explained that .NET Framework 4.5.2 and higher versions have a so-called "quirking" feature. This quirking feature "maintains the semantics of earlier versions" of the .NET Framework, assuring compatibility.
Microsoft is also claiming that developers likely won't have to recompile or rebuild their applications after upgrading the .NET Framework -- at least when using .NET Framework versions 4.5.2, 4.6 and 4.6.1.
One exception to this accelerated product lifecycle pertains to .NET Framework 3.5 Service Pack 1. Its lifecycle is still based on the product lifecycle of the underlying Windows version used, according to this Microsoft FAQ. Depending on the Windows version used, it'll still be supported after the January deadline.
The Jan. 12, 2016 deadline for .NET 4, 4.5 and 4.5.1 coincidentally is also the same accelerated product support deadline for organizations to move to the latest version of Internet Explorer. For most organizations, this policy change means that they must have migrated to using IE 11 by that Jan. 12 date or they'll lose IE product support. However, the policy just states that organizations need to use the latest version of IE per supported Windows version, so it's a little nuanced. For example, Vista users can still continue to use IE 9 and have a supported browser since IE 9 is the most current browser for that Windows operating system.