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 Halo: Reach helmet attachments for Mariner: Mister Chief, Defiant and OPTREX
 * Six new Halo: Reach chest armors, five of which are new robot arm variants of existing chests and one new:
 * Default [R]
 * UA/Counterassault [R]
 * Tactical/Recon [R]
 * Tactical/Patrol [R]
 * Collar/Grenadier [UA] [R]
 * EXO/TSCS
 * Techsuit customization for Halo 3
 * Two new techsuit options for Halo 3 (GEN2 and GEN2 Tinted)
 * Arm and Leg armor customization for Halo 3
 * Twelve new armor permutations for Halo 3, originally from Halo Online:
 * Air Assault
 * Aviator
 * Compass
 * Deadeye
 * Demo
 * Hivemind
 * Navigator
 * Pioneer
 * Soldier
 * Suture
 * Tanker
 * Warrior
 * 26 new weapon skins and 1 new vehicle skin for Halo 3
 * 8 for the BR55HB battle rifle
 * 2 for the SRS99D-S2 AM sniper rifle
 * 1 for the M41 SPNKR
 * 2 for the MA5C assault rifle
 * 2 for the M6G magnum
 * 3 for the M7 SMG
 * 1 for the Type-33 fuel rod gun
 * 1 for the Type-33 needler
 * 1 for the Type-25 plasma pistol
 * 1 for the Type-25 plasma rifle
 * 3 for the Type-51 carbine
 * 1 for the M274 Mongoose