diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index 4dcbe74c5d868..35c88d544c985 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -178,7 +178,7 @@ Performance improvements
 - Performance improvement in :meth:`RangeIndex.take` returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57445`)
 - Performance improvement in indexing operations for string dtypes (:issue:`56997`)
 - :meth:`Series.str.extract` returns a :class:`RangeIndex` columns instead of an :class:`Index` column when possible (:issue:`?``)
-- Performance improvement in ``DataFrameGroupBy.__len__`` and ``SeriesGroupBy.__len__`` (:issue:``)
+- Performance improvement in ``DataFrameGroupBy.__len__`` and ``SeriesGroupBy.__len__`` (:issue:`57595`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.bug_fixes:
diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index dade1a985257d..d02e22c29159f 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -151,7 +151,7 @@ def test_len_nan_group():
 
 @pytest.mark.parametrize("keys", [["a"], ["a", "b"]])
 def test_len_categorical(dropna, observed, keys):
-    # GH#??
+    # GH#57595
     df = DataFrame(
         {
             "a": Categorical([1, 1, 2, np.nan], categories=[1, 2, 3]),