The Saturnine Codex does NOT contain the game rules. It may contain game elements like stats for foes and monsters, though. It is a setting book focused on the world of the City on the Saturnine, the first setting for Dark. The codex will combine information from the House Book and additional information developed for Dark adventures into a new book that brings that setting to life. I expect everything in it will eventually be released in PDF, in one form or another, but not everyone gets one of these hand-bound editions.
Depending on demand, we may offer up additional codices in the future.