Microsoft’s latest wave of backwards compatible titles included four Halo titles, closing the loop on the Halo series’ Xbox 360 library without needing to buy Master Chief Collection.
The four titles are Halo: Combat Evolved Anniversary, Halo 3, Halo 3: ODST, and Halo 4. Halo: Reach had already been in a previous wave of backward compatible titles, but had to be patched after the initial wave lead to a backlash. Now, as long as you have the original disc or own the game digitally, you have access to the game on the Xbox One.
Since Halo 3: ODST is not included in the Master Chief Collection, as it does not star Master Chief, so this is the first chance to play that game on the Xbox One. You can find a full list of backwards compatible titles here.