If memory serves me correctly, ever since dicts became ordered the OrderedDict simply became a subclass of dict, so it will have exactly the same performance characteristics.

OrderedDict was always a subclass of dict maintaining additional information (which is not free, it has to store and manipulate two pointers per entry).

It remains so today, ordereddict is not an alias or trivial facade to the normal dict because it has to maintain its doubly linked list and implement a bunch of additional operations based on that e.g. pop first or move to end.

Yup.

    >>> isinstance(OrderedDict(), dict)
    True

That was already the case in python 2.7 or 3.1.