Comicbook.com has been posting a few articles about Stranger Things 4. First, it's looking more like season 4 will have 9 episodes, not 8. No complaints here.
The bigger question is - will David Harbour's Hopper be returning after seemingly not survived season 3? After completing work on Marvel's Black Widow, he says he has no work lined up yet regarding Stranger Things. He hasn't heard from the show's creators, the Duffer brothers, so now he's not so sure that he is "The American" referenced in the final season 3 episode. To be fair, its unlikely we would see season 4 any time in 2020, so it may be too early to say either way.
Maybe Hopper being "The American" would be too convenient or obvious. But - it's hard to imagine that Hopper really is off the show, so perhaps he'll appear later in the season in some unexpected way?