Mojang has rolled out a snapshot for the forthcoming Minecraft Nether update, and it provides a substantial taste of what's to come in the sizeable patch. Snapshots are basically test versions of forthcoming updates—to access them you'll need to enable snapshots in the Minecraft launcher menu.
So what's in this snapshot? The highlight is three new Nether biomes in the form of the Crimson Forest, Soulsand Valley and Warped Forest. There's also a new high-level material in the form of Netherite, which is refined from Ancient Debris found deep in the Nether's underground. Netherite has a handful of useful effects, one of which is Netherite infused items becoming basically immune to lava – they'll float on the surface, rather than sink.
Expect to find Hoglins as well, though apparently these new creatures "don't do much yet" – maybe one day they'll kill you? There are also more than a dozen new blocks including Crimson Stems and Weeping Vines, the latter of which grows from the bottom of a block downwards.
The full details of the snapshot are available over here, where you'll find more specifics on the new biomes—the Crimson Forest sounds especially cool, promising as it does "all kinds of strange new vegetation". Take note that using snapshots can corrupt your world, so Mojang advises backing your world up (or running snapshots in a separate folder) if you want to get involved.
For a history of what's been added to Minecraft recently, head over to our log of Minecraft updates.