Actors are communicating via asynchronous messages. Never share state. An actor is single threaded.
Each thread can run multiple actors concurrently, but a single actor is in a single thread. There are two additional advantages of this model: CPU utilization within a single computer and the ability to distribute the workload to several computers.
In the cloud things get even more complicated regarding distributed computing.
New Actor types:
Actors are actually Nanonservices very similar to Microservices
Microservices is an organizational decision, not so much a technical decision.
Base the communication on Interfaces instead of Messages.