It still has no release date yet, alas.
Developer ConcernedApepostedthe “sneak peek” to X (formerly Twitter).
Stardew Valley currently supports four-player multiplayer, a feature which was addedback in update 1.3.

Doubling the player count several years later is just delightful.
ConcernedApe last teased update 1.6back in July, with far fewer details.
The update itself was announcedback in April.