What is the threading model of self-hosted Katana?

Simple question here, in theory... If I'm using self-hosting in Katana (i.e. Microsoft.Owin.Hosting), what assumptions can I make about the threading model and reentrancy? Should I be expected to handle requests concurrently on multiple processor threads, or is there some sort of event loop?

The relevant class for launching a self-hosted web app in Katana is http://ift.tt/2wo67Gi.