In my understanding, it's hard to say. It appears to have a base semantics that you can think through as OO-like message passing or FP-like lambda calculus reduction. I assume it's implemented OO-style on the JVM, but it's hard to say whether the core language biases one side or the other.

I think that's interesting but also a big indicator of why you see such a big split-brain situation in Scala. FPers program FP-Scala, OOers program OO-Scala, but neither is dominating. As far as I can tell, Martin Odersky programs balanced OO-FP, but few others do.

scala is the unholy child of everything from oo and everything from fp (well, almost).

(but i found it hard enough to program in ocaml, which is similar to f#, because i was always torn between oo and fp parts, so maybe i am biased or just Too Dumb For Scala)