Tokio is about being flexible (true today, even more true in the upcoming release). It is more about set of primitives that you can assemble in a way that fits your needs. You can structure the concurrency of your application however you want.

So...

> High I/O systems usually spawn multiple reactors, e.g. one reactor per CPU core.

Depends on what you are calling multiple reactors. If you mean a loop that responds to events and run tasks, then yes. For example, you can plug in [this](http://github.com/carllerche/futures-pool) as the task executor and get a multi threaded, work stealing, scheduler.

Or, maybe you are talking about OS level selectors (epoll), in which case you are going to run up against OS limitations.

libevent2 (which tokio is very similar to) has the same constraint:

> Currently, only one thread can be dispatching a given event_base at a time. If you want to run events in multiple threads at once, you can either have a single event_base whose events add work to a work queue, or you can create multiple event_base objects.

http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html/