Microsoft is apparently skipping an entire version when it moves from the just released .NET Core 3.0. According to the company…
While there will be a .NET Core 3.1 update release (slated for November 2019), the next full version update to .NET Core will be .NET 5.0.
Additionally, the Core component of the name will be removed…
As you can see “Core” will be removed from the name because .NET 5 will produce a single runtime and framework that can be used anywhere!
Full announcement: .NET Core 3.0 Released / .NET 5 is vNext