An open beta for the much-anticipated Halo Wars 2 will reportedly take place next week, between the June 13-20. This news comes via Major Nelson's Xbox Live profile, which states that he is following 'Halo Wars 2 Open Beta.'
Further checking found that it leads to a store page for the beta, which will apparently run through E3 next week.
This is the first we've seen or heard regarding an open beta for the game, so it's possible that the announcement was meant to come as a surprise during their briefing.
You can also see a bunch of screens that were just posted on Imgur.