https://blogs.msdn.microsoft.com/dotnet/2018/11/05/announcing-net-standard-2-1/

Since we shipped .NET Standard 2.0 about a year ago, we’ve shipped two updates to .NET Core 2.1 and are about to release .NET Core 2.2. It’s time to update the standard to include some of the new concepts as well as a number of small improvements that make your life easier across the various impl...