When and where do I require files in a rails application?

Have you tried removing it from the first model as well? I believe Rails will automatically load any files you have in your lib directory without you ever having to require them explicitly.

This is a helpful post about this issue.

In short, Rails autoloads classes in your lib directory only if they follow the proper naming conventions.

I would generally place that require statement in a config/initalizer file, e.g. config/initializers/load_proxy.rb