talking about it beats guessing, so just bring it up casually. you don't need some formal "state of the union" conversation - could be as simple as "hey, i'm really enjoying this and i'd like to keep seeing you without the app in the mix" next time you're hanging out. four dates is definitely enough to know if there's real potential worth exploring without the distraction of other matches.
the tricky part is that deleting the app doesn't automatically mean exclusivity - it just means you're both stepping back from actively looking. some people delete it early as a gesture of good faith, others wait until there's an explicit conversation about being exclusive. neither is wrong, but being on the same page matters way more than the timing. if they seem into you (which it sounds like they are), they'll probably appreciate you taking that first step instead of both of you awkwardly waiting for the other person to do it.