The letter was sent to DirectX and XNA MVPs, select developers who are influential in the development communities surrounding Microsoft's tools and platforms.
"Presently the XNA Game Studio is not in active development and DirectX is no longer evolving as a technology," the letter said.
"As a result, effective [from] April 1, 2014 XNA/DirectX will be fully retired from the MVP Award Programme."
Portions of the letter were posted on the blog of developer Promit Roy, who notes that DirectX could still continue through the Direct3D API, which is likely to be absorbed as a core part of Windows rather than a separate toolset.
As for XNA Game Studio, Microsoft says it will continue to support games developed with XNA on Xbox 360, Windows and WIndows Phone, but confirmed that there are "no plans for future versions of the XNA product".
XNA was best known as the development tools used for games released through the Xbox Live Indie Games platform like Cthulhu Saves the World and Escape Goat.
It has also been widely used in Xbox Live Arcade and PC games including Bastion, Fez, Dust: An Elysian Tail, Terraria and Magicka.
Watch a trailer for Fez - created with XNA - below: