During AX 2009, we introduced ASP.net based EP framework which brings in tons of value such AJAX out of the box, rich and responsive controls, power of .net etc. We kept the old X++ Web framework in the product for one release to help the partners and customers migrate to the new framework. Now we have published the discontinuation notice in customer source / partner source. In the next version of AX, only asp.net based web user interface will be shipped.

 https://mbs.microsoft.com/partnersource/newsevents/news/newsgeneral/ax_epuiframework.htm  

 https://mbs.microsoft.com/customersource/newsevents/news/generalnews/ax_epuiframework.htm