Halo Wars: Definitive Edition is definitely heading to Steam
 

Check outside for airborne pigs, cows returning home, and Beelzebub on a sled. Among all the other things about 2017 that were inconceivable just a year ago, a Halo game is now coming to Steam. Microsoft announced that the remastered version of the 2009 RTS Halo Wars is hitting Valve's game shop on April 20, in addition to its standalone release on the Windows store.

http://techreport.com/news/31753/hal...ading-to-steam