By default, Pykka builds on top of Python's regular threading concurrency model, via the standard library modules threading and queue.
Pykka 2 and earlier shipped with some alternative implementations that ran on top of gevent or eventlet. These alternative implementations were removed in Pykka 3.
Note that Pykka does no attempt at supporting a mix of concurrency runtimes. Such a future feature has briefly been discussed in issue 11.
threading