Note that it's not either/or - you can dispatch work from an event loop to a thread pool (or a process pool) with loop.run_in_executor [0], while loop.call_soon

Note that it's not either/or - you can dispatch work from an event loop to a thread pool (or a process pool) with loop.run_in_executor [0], while loop.call_soon_threadsafe [1] can be used by worker threads to add callbacks to the event loop. This means that the "frontend" of a service can be asyncio, allowing it to support features like WebSockets that are non-trivial to support without aiohttp or a similiar asyncio-native HTTP server [2], while the "backend" of the service can be multi-threaded or multi-process for CPU-bound work. 0: https://docs.python.org/3/library/asyncio-eventloop.html#executor https://docs.python.org/3/library/asyncio-eventloop.html#exe... 1: https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.AbstractEventLoop.call_soon_threadsafe https://docs.python.org/3/library/asyncio-eventloop.html#asy... 2: Flask-SocketIO, for example, requires that you use eventlet or gevent, which are the "legacy" ways of doing asynchronous IO: https://flask-socketio.readthedocs.io/en/latest/ https://flask-socketio.readthedocs.io/en/latest/