According to the spec:

the returned value can be either an immutable collection or an immutable iterator

Currently, we return a dict (link):

correlations = get_value(_CORRELATION_CONTEXT_KEY, context=context)
if isinstance(correlations, dict):
    return correlations.copy()
return {}

This was mentioned in the PR but not definitively addressed #471 (comment), so I thought it might be worth bringing up again before GA.