.NET 5.0 is the first release in our .NET unification journey. We built .NET 5.0 to enable a much larger group of developers to migrate their .NET Framework code and apps to .NET 5.0. We’ve also done much of the early work in 5.0 so that Xamarin developers can use the unified .NET platform when we release .NET 6.0. There is more on .NET unification, later in the post.

System.Text.Json

There were significant improvements made to the System.Text.Json library for .NET 5, and in particular for JsonSerializer, but many of those improvements were actually ported back to .NET Core 3.1 and released as part of servicing fixes (see dotnet/corefx#41771). Even so, there are some nice improvements that show up in .NET 5 beyond those

NET 5.0 is the main implementation of .NET going forward and .NET Framework 4.x is still supported.

.Net 5.0

System.Text.RegularExpressions

The System.Text.RegularExpressions namespace has been in .NET for years, all the way back to .NET Framework 1.1. It’s used in hundreds of places within the .NET implementation itself, and directly by thousands upon thousands of applications. Across all of that, it represents a significant source of CPU consumption.