In erlang based systems stateful network protocols and concurrent user stories are all modeled with actors and one million connections per node for websockets is a thing.

I deployed an actor-based system model to completely rearchitect and replace an inefficient stateless python system. There have been zero runtime or concurrency errors since I deployed (unfortunately sometimes the hardware the actors are modeling fail us) but patches to work around the hardware failures are simple.

The Actor Model has been used in many important large applications [Bernstein, Bykov, Geller, Kliot, and Thelin 2014; Bonér and Reisz 2017, Cesarini 2019] and has become the foundation for current computing.

Satisfactory implementation for Reusable Scalable Intelligent Systems with millions of Actor cores for quadrillions of Actor are under development, but not yet publicly available.