undefined method `insert'

[ChrisCPO]

using rails-5.1.4
using grape-1.0.3

Documentation says I can

class API < Grape::API
  use Overwriter
  insert_before Overwriter, CustomOverwriter, message: 'Overwritten again.'
  insert 0, CustomOverwriter, message: 'Overwrites all other middleware.'

  get '/' do
  end
end

Yet when I have:

class API::Application < Grape::API
  prefix 'api'
  format :json
  formatter :json, Grape::Formatter::Roar
  default_error_formatter :json

  helpers API::V1::Helpers

  use API::Utf8Sanitizer
  insert 0, API::Utf8Sanitizer
  insert_before Grape::Middleware::Error, API::Logger

  mount API::V1::Application
end

I'm getting:

NoMethodError: undefined method `insert' for API::Application:Class
Did you mean?  inspect

[dblock]

This seems to have been added in 1.2.0, #1787