Akka has two types of actors: typed and untyped. Typed actors allow the compiler to type check messages, while untyped (or classic actors) perform runtime checking. This also means references to actors can be typed, so if you have multiple implementations of actors that implement the same protocol, you can substitute between the different actors and verify the protocol at compile time.
https://doc.akka.io/docs/akka/current/typed/from-classic.htm...
I had played with Erlang before using Scala/Akka, so untyped actors were a familiar experience. My team decided to use typed actors going forward after an Akka version update since that seems to be the strategic direction of Akka (and it does help to have the compiler complain if we try sending a message that the actor doesn't understand).