For quite some time there’s been a lot of fan speculation that Lars is AFAB and trans, with quite a lot of compelling evidence to that effect. It’s a thing I absolutely believe and I keep on hoping for confirmation in-show.
So, the Very Trans Narrative ending of Season 5 could lead to a future episode (or the upcoming movie) to finally answer this.
Here’s how I think it might happen.
Spoilers for Season 5
Lars: So, Steven… you are actually your mom?
Steven: Well, sort of, like… I was her, and then she became me.
Lars: So you were born… a girl? And now you’re a boy?
Steven: Yeah! Well, sort of. Gems don’t technically have a gender, but–
Lars: What I mean is… do you think a human could do that too?
Steven: I don’t see why not.