These are the changes in pandas 2.1.1. See :ref:`release` for a full changelog including other versions of pandas.
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- Fixed regression in :func:`merge` when merging over a PyArrow string index (:issue:`54894`)
- Fixed regression in :meth:`DataFrame.__setitem__` raising
AssertionErrorwhen setting a :class:`Series` with a partial :class:`MultiIndex` (:issue:`54875`)