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If it fits on a line then it seems Counter's repr is used:
 >>> pprint(Counter({i:i*i for i in range(10)}))
 Counter({9: 81, 8: 64, 7: 49, 6: 36, 5: 25, 4: 16, 3: 9, 2: 4, 1: 1, 0: 0})
Otherwise It is shown as a dict (Counter is a dict subclass) if it is too 
large (multi-line):
 >>> pprint(Counter({i:i*i for i in range(10)}), width=20)
 {0: 0,
 1: 1,
 2: 4,
 3: 9,
 4: 16,
 5: 25,
 6: 36,
 7: 49,
 8: 64,
 9: 81}
 
the behaviour is weird but pprint doesn't promise that custom objects such 
as Counter that can't be created using Python literals will be printed in a 
reversible manner.
It seems there is a special support for some objects:
 >>> pprint(frozenset({i for i in range(10)}))
 frozenset({0, 1, 2, 3, 4, 5, 6, 7, 8, 9})
 >>> pprint(frozenset({i for i in range(10)}), width=20)
 frozenset({0,
 1,
 2,
 3,
 4,
 5,
 6,
 7,
 8,
 9})
Perhaps the support for Counter could be added using functools.singledispatch
and/or __prettyprint__ hook from issue #7434