The problem: We need to be able to specify configuration in a way that can be inherited to models that include ActiveRecord::Model. So it is no longer sufficient to put 'top level' config on ActiveRecord::Base, but we do want configuration specified on ActiveRecord::Base and descendants to continue to work. So we need something like class_attribute that can be defined on a module but that is inherited when ActiveRecord::Model is included. The solution: added ActiveModel::Configuration module which provides a config_attribute macro. It's a bit specific hence I am not putting this in Active Support or making it a 'public API' at present.