Stardew Valley's next update will bring a new major festival, support for 8-player multiplayer, and over 100 new lines of dialogue. It still has no release date yet, alas.
Developer ConcernedApe posted the "sneak peek" to X (formerly Twitter). The full list of additions also includes two mini festivals, new late-game content which expands on "each of the skill areas", new items and crafting recipes, and winter clothing for the villagers.
Stardew Valley currently supports four-player multiplayer, a feature which was added back in update 1.3. Doubling the player count several years later is just delightful.
ConcernedApe last teased update 1.6 back in July, with far fewer details. The update itself was announced back in April. At the time, ConcernedApe - aka Eric Barone - said that the update was "mostly changes for modders (which will make it easier & more powerful to mod)." It sounds as if it has grown in scope since then, as Stardew Valley updates have a tendency to do.
Update 1.6 is also being worked on as a break from Barone's next game, Haunted Chocolatier, which looks like a spooky, more combat-focused sibling to Stardew Valley's pastoral farm sim.