Nowadays, post-credits scenes are as common as the superhero movies that popularized them, and even TV shows are getting in on the action.
Despite the fact that Season 1 and Season 2 of Stranger Things didn’t contain any bonus scenes, Stranger Things Season 3 does include a post-credits (or technically mid-credits) scene after the finale ends, so when you start to see snow floating across the credits, don’t click away or let Netflix autoplay whatever’s next on your list, since there’s a fairly major reveal halfway through that seems to set up Season 4.
Source: IGN.com Does Stranger Things Season 3 Have a Post-Credits Scene?