In actual practice... ractors are kind of still new experimental technology, that are hard to use if you are using any existing gem code. And fibers are not ne

In actual practice... ractors are kind of still new experimental technology, that are hard to use if you are using any existing gem code. And fibers are not new, but also can be hard to use and aren't super popular in general use. So the practical answer is you probably won't use either. :) But one way to explain the difference is that fibers are basically for cooperative/evented concurrency, while ractors are a new invention that are more like (OS native) threads but without shared memory.