TL;DR: ReSharper 2018.2 will require having .NET Framework 4.6.1 installed.
Starting with the next ReSharper 2018.2 release, we will require having .NET Framework 4.6.1 installed on your machine. Earlier versions of ReSharper will continue to work on .NET Framework 4.5.
Why is this changing?
With the .NET Framework evolving rapidly in the past years and Microsoft having stopped support for .NET Framework 4, 4.5 and 4.5.1 over two years ago, updating the required .NET runtime for ReSharper is a logical next step.
Newer versions of the .NET Framework come with numerous improvements, such as performance, security and Windows Presentation Foundation updates. The NuGet client SDK used by ReSharper also requires .NET Framework 4.6 or higher. Making use of the newer, modern runtime brings along these improvements and will greatly benefit our users and opens up new possibilities!
Thanks to this upgrade, the ReSharper codebase can now target .NET Standard 2.0 (and .NET Core), so that for example our Command Line Tools and Remote Profiling Tools will eventually no longer require a full .NET Framework installation at all. This also helps our (non-UI) tools to run on Linux and Mac OS X with better quality. The future is bright!