Fans of Games Workshop's dark sci-fi war game, Warhammer 40k, are not exactly spoiled for content. There are plenty of armies to choose from, many of which have been getting consistent updates and additions. The orks have their Beast Snaggas, the Sisters of Battle have brand new battle apparatuses, and the Adeptus Custodes are getting a new battle box. Now, another army, specifically the utopian mech suit pilots of the Tau Empire, will be getting a new Codex.
In an official post on the Warhammer Community website, Games Workshop teased changes coming to Warhammer 40k's Tau. First, the post mentions the release of a brand new Kill Teams box for the Tau: Chalnath. This would include new terrain, a rulebook, and new miniatures for both the Tau and the Adeptus Sororitas. This is followed up by the announcement of a brand new codex coming for the blue-skinned army coming early next year.

The post continues with a few more details. First they tease with new artwork for the book. Specifically it shows off a Tau Commander's Enforcer Battlesuit leading the charge in a massive battle against a mob of orks. Thankfully, since pulse rifles and pulse carbines have gotten an overhaul recently, this makes this hypothetical battle less of a death wish for the Tau and more of an even fight.
As for additional details, Games Workshop were coy. They have teased new things coming down the line for the Tau's Pathfinder units, including the reveal of a new subcommander called Darkstrider, but anything beyond this new artwork and a rough release window, not much else is known. However, Games Workshop does mention that the new codex for the Tau would be available around the same time as the new codex releases for both the Adeptus Custodes and the Genestealer Cult armies. Thankfully, this makes the release window of early 2022 seem a little less nebulous.