The lesson Build a Codex model with XML includes out-of-date syntax for associating a model with a datastream. It seems ActiveFedora 10.0.0 renamed contains to has_subresource and that it simply removed the delegate_to: functionality on property (commit here).
I'm new to Hydra but I'd be happy to update the tutorial if I knew what new functionality was intended to replace this. The deprecation message referenced "Forms" – is this still used in Hydra 11? Where can I find documentation on this?