According to a blog post on Halo Way Point, 343 Industries is getting ready to release a huge update for Halo: The Master Chief Collection and is in the “final stages of testing”.
“Over the past few weeks, we’ve been completing work on the upcoming content update, which will improve stability, matchmaking, the party and invite system, and more,” it announced. “As we announced previously, this content update includes fundamental changes to the aforementioned systems, and making and validating these changes requires substantial time beyond what was required for prior updates.
We’re happy with the progress on the next CU, with significant progress being made on big and small issues, and we’re being diligent in gameplay and stress testing to ensure that it is a meaningful update. While we haven’t yet locked an exact release date of this CU, the work is in its final stages of testing and bug squashing is well underway. The next time we communicate regarding the status of the upcoming CU, we will provide a definitive timeframe for its availability.”
343 originally began to beta test for MCC due to the scale of the update” and “to ensure the official release is the best possible experience for all players”, though this was later rethought and axed.