Example of changing the utility navigation in the layout (Top right of nav bar)

active_admin.rb

# This assumes you are using that you are using Active Admin from master.
# You can do this with 0.4.2 but you would need to override the HeaderRenderer instead

# config/initializers/active_admin.rb
ActiveAdmin.setup do |config|

  # View a list of all the elements you can override
  # https://github.com/gregbell/active_admin/blob/master/lib/active_admin/view_factory.rb
  config.view_factory.utility_navigation = MyCustomUtilityNav

end

# The subclass the utility nav
class MyCustomUtilityNav < ActiveAdmin::Views::UtilityNav
  
  # Override the build method which accepts the current ActiveAdmin::Namespace
  def build(namespace)
    span("Hello From My Utility Nav")
    super(namespace)
  end

end

# OR Create a whole new utility nav

class MyCustomUtilityNav < ActiveAdmin::Component

  def build(namespace)
    span("Hello From My Utility Nav")
  end

  def tag_name
    'p'
  end

end

Never mind, this works as expected. I was experiencing the problem because I had tried to scope ActiveAdmin within routes.rb, which messed up the paths.

I had tried this:

scope '/admin', as: :admin do
  ActiveAdmin.routes(self)
end

And was registering some resources with namespace: false so I could have other namespaces nested within /admin/. I still don't have a good solution for doing that, but I'm just using other routes for now.