The docs claim PyPy ignores hash randomization:
Hash randomization (-R) is ignored in PyPy. In CPython before 3.4 it has little point.
However, after asking on IRC, it appears pypy3 does use SipHash by default (presumably with a randomized key), but still ignores the -R flag (which doesn't matter because it's on by default).
mjacob from IRC:
we didn't follow CPython in implementing their first (unsuccessful) attempt to fix the problem however we followed CPython in implementing the second attempt to fix the problem with a cryptographic hash function (see also sys.hash_info)
I think the cpython_differences doc should be updated to say this is not an issue in pypy3 (if this information is correct).