Previews of IronPython for .NET 4 have been shipping along with VS 2010, but that does not mean the two are tied together. While Microsoft intends to launch IronPython for .NET 4 and Visual Studio 2010 on the same day, they will remain on separate development cycles for the foreseeable future.

IronPython for .NET 4 will be compatible with Python 2.6. There are currently no definite plans for supporting Python 3.1. Python 3.1 is a significant break from the 2.x series. In addition to significant improvements over earlier versions of the language, it will remove many features that are no longer considered to be desirable. This means Python 3.1 is not backwards compatible, which in turns has lead to a slow adoption for Python 3.1.

The final version of IronPython for .NET 4.0 will support C#’s new dynamic keyword as well as the improved version of VB’s implicit late binding.

Editor's note - This article originally discussed Python 3.1 support based on information gleaned at an IronPython presentation in Copenhagen. That information was incorrect, and there is in fact no confirmed date for 3.x compatibility according to the timeline at DevHawk. The article above has been updated to reflect this