diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 571fcc67f3bb5..69ff4006f34f3 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -5175,10 +5175,16 @@ def _dir_additions(self):
         add the string-like attributes from the info_axis.
         If info_axis is a MultiIndex, it's first level values are used.
         """
+        unique_entries = self._info_axis.unique(level=0)
+        if len(unique_entries) > 1000:
+            unique_entries = unique_entries[:1000]
+            warnings.warn(
+                "Completion only considers the first 1000 entries "
+                "for performance reasons",
+                UserWarning,
+            )
         additions = {
-            c
-            for c in self._info_axis.unique(level=0)[:100]
-            if isinstance(c, str) and c.isidentifier()
+            c for c in unique_entries if isinstance(c, str) and c.isidentifier()
         }
         return super()._dir_additions().union(additions)
 
diff --git a/pandas/tests/series/test_api.py b/pandas/tests/series/test_api.py
index 042841bb4e019..bcf5adf084df3 100644
--- a/pandas/tests/series/test_api.py
+++ b/pandas/tests/series/test_api.py
@@ -248,7 +248,7 @@ def get_dir(s):
             tm.makeIntIndex(10),
             tm.makeFloatIndex(10),
             Index([True, False]),
-            Index([f"a{i}" for i in range(101)]),
+            Index([f"a{i}" for i in range(1001)]),
             pd.MultiIndex.from_tuples(zip("ABCD", "EFGH")),
             pd.MultiIndex.from_tuples(zip([0, 1, 2, 3], "EFGH")),
         ],
@@ -256,9 +256,14 @@ def get_dir(s):
     def test_index_tab_completion(self, index):
         # dir contains string-like values of the Index.
         s = pd.Series(index=index, dtype=object)
-        dir_s = dir(s)
+        if len(s) < 1000:
+            dir_s = dir(s)
+        else:
+            with tm.assert_produces_warning(UserWarning):
+                dir_s = dir(s)
+
         for i, x in enumerate(s.index.unique(level=0)):
-            if i < 100:
+            if i < 1000:
                 assert not isinstance(x, str) or not x.isidentifier() or x in dir_s
             else:
                 assert x not in dir_s