From Halopedia, the Halo wiki
HIVEMIND is an armor set intended for use by Spartan personnel assigned to Flood containment operations. It was tested at ANVIL Station, which was considered an ideal testing ground for such equipment.
The Hivemind armor set was first introduced into Halo 3's MCC port along with eleven other new armor sets, as part of Season 5: Anvil. It was never available in Halo 3 for Xbox 360. The set is one of six which do not have any associated forerarm armor.
The HIVEMIND armor set was originally created as a useable armor permutation for Halo Online, a cancelled Halo 3-derived multiplayer game developed by Saber Interactive and Innova Systems which was intended to be released exclusively in Russia for the PC. After the game's cancellation in 2016, the armor was one of twelve sets introduced to Halo 3 in The Master Chief Collection as part of the game's fifth season in 2021.
List of appearances