A couple of people on NeoGAF were able to find information about Halo Wars 2 that wasn’t suppose to be there. According to the Xbox Store, an open beta for Halo Wars 2 will take place from June 13-20. The beta will also have a download size of 13GB.
This more than likely means that an official announcement is supposed to take place during Microsoft’s E3 Press Conference.
Halo Wars 2 will be released this Fall for PC and Xbox One.