There is a conversion.  See builtin___build_class__ in Python/bltinmodule.c (and the LOAD_BUILD_CLASS target in Python/ceval.c).  Specifically, the metaclass (e.g. the builtin type) is instantiated using the namespace from the class definition.  The metaclass copies that namespace into a new dict.  So the following two bits of code are equivalent:

  # using a class definition

  ns = OrderedDict()

  class Meta(type):
      def __prepare__(*args, **kwargs):
          return ns

  class Spam(metaclass=Meta):
      a = 1
      b = 2
      ns.move_to_end('a')

  # using the metaclass directly

  ns = OrderedDict()
  ns['a'] = 1
  ns['b'] = 2
  ns.move_to_end('a')
  Spam = Meta('Spam', (object,), ns)

In both cases Spam.__dict__ will be a proxy for a new dict copied from ns.