diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index ad644bb3128809..9cd73cc42510e7 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -7561,6 +7561,23 @@ def test_with_module(self):
         typing.evaluate_forward_ref(
             fwdref_module.fw,)
 
+    def test_evaluate_forward_ref_string_format(self):
+        # Test evaluating forward references in STRING format
+        # does not 'leak' internal names
+        # See https://github.com/python/cpython/issues/150641
+        from annotationlib import Format, get_annotations
+
+        def f(arg: unknown | str | int | list[str] | tuple[int, ...]): ...
+
+        ref = get_annotations(f, format=Format.FORWARDREF)['arg']
+        self.assertEqual(
+            typing.evaluate_forward_ref(ref, format=Format.STRING),
+            "unknown | str | int | list[str] | tuple[int, ...]",
+        )
+        self.assertEqual(
+            typing.evaluate_forward_ref(ref, format=Format.STRING),
+            ref.__resolved_str__
+        )
 
 class CollectionsAbcTests(BaseTestCase):
 
diff --git a/Lib/typing.py b/Lib/typing.py
index 715d08e0e1603e..b2bc52e55d0fc7 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1019,7 +1019,7 @@ def evaluate_forward_ref(
 
     """
     if format == annotationlib.Format.STRING:
-        return forward_ref.__forward_arg__
+        return forward_ref.__resolved_str__
     if forward_ref.__forward_arg__ in _recursive_guard:
         return forward_ref
 
diff --git a/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst b/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst
new file mode 100644
index 00000000000000..3b9a3cbb3c2c26
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-31-14-39-25.gh-issue-150641.LLIhd1.rst
@@ -0,0 +1,2 @@
+Fix evaluating forward references in STRING format can 'leak' internal names
+in ``typing``.