New changes are coming to Warhammer 40k. These aren't rules changes done in small increments like their recent dataslates, neither is it the announcement of a new codex. Instead, the very structure of Warhammer 40k's content going forward is going in a different direction for 2022: seasons.
As the official Warhammer-Community post explains, Warhammer 40k seasons will focus on different locations and venues of the grimdark sci-fi universes. These seasons will last six months and include campaign books, mission packs, and even battleboxes. Furthermore, it will cover all content, both casual and competitive going forward.
This inaugural Warhammer 40k season will be called Nachmund. Named after the Nachmund Gauntlet, players will return to Vigilus where Imperium forces continue to hold against the forces of Chaos. This battle can be played out with the new campaign book, Vigilus Alone. Similar to the War Zone Octarius books, it will feature new army rules, Crucible rules, as well as an Army of Renown and a Codex Supplement. Along with the campaign book, there will be a new Crusade mission pack, featuring 24 new missions, extra Requisitions, Agendas, and Battle Traits, and a new War of Faith campaign system to help link prior Vigilus campaign books together into a larger narrative.
As for those more geared towards competitive play, this Warhammer 40k season includes new Grand Tournament mission packs. These will include new mission objectives as well as adjusted point costs for armies.
Finally, the newly announced battlebox, Eldritch Omens, as well as two upcoming Kill Teams boxes will be included as a part of of this new season. Games Workshop has mentioned that this entire season of content will not focus on just the Imperium and Chaos forces however. For example, Eldritch Omens includes new Aeldari forces. Furthermore, Vigilus is one of the most highly strategic locations in the universe of Warhammer 40k; just about every single faction has a stake in wanting to to capture or hold it.
Given the immense popularity of seasonal content models, Warhammer 40k adopting this thematic structure for its content makes sense on paper. It will help give players a better idea of what will be coming down the line as well as make the community as a whole feel more connected through shared emergent experiences on the war table. As for how that will work in practice, only time will tell.