Series 5: Anvil

Season 5 is an upcoming season for Halo: The Master Chief Collection, expected to be released some time in January 2021. 343 Industries intends to release the previously-cut AKIS and Mariner helmets as part of this update, after they were pushed back from Season 4 due to difficulties encountered during development.

Season unlocks
Season 5 is expected to add the following content to the game:
 * 2 new Halo: Reach helmets: AKIS, Mariner
 * 3 Halo: Reach helmet attachments for AKIS: GRD, CBRN, GRD/CBRN
 * 3 unidentified Halo: Reach helmet attachments for Mariner