diff --git a/Doc/library/collections.abc.rst b/Doc/library/collections.abc.rst
index 0abc87f919d..2c941b47748 100644
--- a/Doc/library/collections.abc.rst
+++ b/Doc/library/collections.abc.rst
@@ -104,6 +104,9 @@ example, knowing that a class supplies ``__getitem__``, ``__len__``, and
 ``__iter__`` is insufficient for distinguishing a :class:`Sequence` from
 a :class:`Mapping`.
 
+.. versionadded:: 3.9
+   These abstract classes now support ``[]``. See :ref:`types-genericalias`
+   and :pep:`585`.
 
 .. _collections-abstract-base-classes:
 
diff --git a/Misc/NEWS.d/next/Documentation/2021-10-19-01-41-40.bpo-45449.fjHZJc.rst b/Misc/NEWS.d/next/Documentation/2021-10-19-01-41-40.bpo-45449.fjHZJc.rst
new file mode 100644
index 00000000000..fb817757a14
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2021-10-19-01-41-40.bpo-45449.fjHZJc.rst
@@ -0,0 +1 @@
+Add note about :pep:`585` in :mod:`collections.abc`.