Halo 5 is getting the "true 4K" treatment with the Xbox One X. During Halo 5's pre-release hype cycle, Microsoft said that it was so focused on hitting 60 frames per-second with the game that there weren't any sacred cows -- including split-screen co-op, a series staple. Maybe don't expect that to return with the Xbox One X's more powerful innards, though.
More than that, by year's end, Halo: Combat Evolved Anniversary, Halo 3, Halo 3: ODST and Halo 4 will all be backwards compatible on Xbox One. You know, if you didn't already own the Halo: The Master Chief Collection of remasters. In a blog post, Microsoft says that every Xbox 360 add-on map pack will be made free on the Xbox Store. You'll even be able to hook an Ethernet cord between Xbox Ones and Xbox 360s for a cross-generation LAN party if you're so inclined.
Microsoft is easing even more for this year (2017 is Halo 3's 10th anniversary, after all) and you can catch all the details at the source link below.