The news that cooperative campaign play and Forge features would be missing at release was announced during a Halo Infinite development update from 343.
According to head of creative Joseph Staten, the team found more time is needed to complete some of the game's features ahead of release as some are not up to standard.
With the game being a live service, the features can be released once they have been "in the oven" for a bit longer.
"As we focused the team for shutdown and really focused on a quality experience for launch, we made the really tough decision to delay shipping campaign co-op for launch," said Staten. "And, we also made the tough call to delay shipping Forge past launch as well.
"We are going to keep campaign co-op and Forge in the oven for a little bit longer, and then when they are ready, we are going to release them as part of our seasonal roadmap next year."
Staten said campaign co-op will now launch during Season 2, and Forge will arrive during Season 3, with each season lasting around three months.
Another feature also seeing a delay is split-screen multiplayer for PC.
The team is currently addressing things which cropped up during the multiplayer Technical Preview, like bugs and whatnot. Insiders can expect the next multiplayer test soon, and it will feature PvP, 4v4,and Big Team matches (thanks, Neowin). After release, Insiders will also get to test Forge following the core game launch.
Halo Infinite will be released this holiday for PC and Xbox consoles, and 343 says it is close to confirming a set date for launch.