A109 Host Kit Status
There's an unofficial draft version of the A109 host-kit on the site. I say "draft" because it's not tested at all. The focus of A108-A109 is on the core and its contexts, not the host-kit.
However, if you do try it, remember that modules have changed; therefore, extension modules have changed! However, the /Core release includes the minimal xtest extension, which seems to work ok, so you can have some degree of confidence.
However, your extension module header should look like this now:
title: "My extension"
A number of other options are available. (See Brian Hawley's notes if you need more info.)