Season 9

Season 9 was a planned season update for Halo: The Master Chief Collection, originally anticipated to release some time in 2021 but later pushed back to 2022. As of December 2020, plans had been laid internally at 343 Industries for this season.

In September 2021, 343 released an MCC Development Update in which they stated that Series 8: Mythic would be the last season released in 2021. In this blog, they also explained that with the release of Halo Infinite in December 2021, they expected the manner in which they delivered MCC content to change, pivoting away from large semi-regular seasonal updates and towards smaller ones that could be delivered as soon as they were ready, depending on development status and the studio's overall roadmap.

The seasonal model within The Master Chief Collection was later shifted to series, marking the official cancellation of Season 9 and 10, with much of their content ultimately released in the Halo 20th anniversary event and the Series 9 update.

Intended content
Internal files within The Master Chief Collection provide some insight as to the content Season 9 was intended to contain. The file which tracks player unlocks,, retains old code comments that refer to Season 9 content, listing much of the Halo: Reach, Halo 3, and Halo 2: Anniversary content ultimately implemented into the game with the Halo 20th anniversary event in late 2021. The content listed under these headings include;

Halo: Reach

 * Blackguard Bishop helmet
 * Utility accessory
 * Hydration Container

Halo 3

 * MIRAGE armor
 * Blackguard Bishop helmet
 * Shoulder accessory
 * Duke
 * Back accessory
 * The Beast
 * Fronkbox
 * Grunt Plush
 * Last Word
 * Rucksack
 * X-Pack
 * OGX weapon skins
 * Assault Rifle
 * Battle Rifle
 * Rocket Launcher
 * Shotgun
 * Magnum
 * Sniper Rifle

Halo 2: Anniversary

 * ORION armor