You have about a year left to experience the online services for seven Halo titles, if you're still playing them on the Xbox 360, or through backwards compatibility. 343 has announced that after many years, and an ever-dwindling playerbase, it's time to "sunset" the servers for Halo: Combat Evolved Anniversary, Halo Wars, Spartan Assault, Halo: ODST, Halo 3, Halo 4, and Halo: Reach. By December 2021, anything involving online will no longer work, which means online matchmaking won't work, certain achievements will no longer be obtainable, filesharing, and other smaller features will be gone for good. Obviously, the singleplayer campaigns of each of the games will still be fully playable offline. This sunsetting also applies to the lineup, even if you're playing them on the Xbox One, or the Xbox Series X|S. Digital copies of all of these games have also been delisted, following the announcement. For those still interested in playing these games online, there's always The Master Chief Collection, or Halo Wars: Definitive Edition, which will both continue to be supported for a long time to come.

Source

Microsoft announces plan to shut down online for Halo titles on the Xbox 360 by next year | GBAtemp.net - The Independent Video Game Community