diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 93b3382b9c654e..856d47be479444 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -7295,6 +7295,31 @@ def test_update_type_cache(self):
             """)
         script_helper.assert_python_ok('-c', script)
 
+    @unittest.skipIf(_interpreters is None, "missing _interpreters module")
+    def test_static_type_concurrent_init_fini(self):
+        # gh-136421: When a managed static extension type is concurrently used
+        # by only subinterpreters, there was a crash due to the runtime state
+        # rather than an interpreter state being updated wrongly by mistaking
+        # the type's first initialization stage or last finalization one.
+        script = textwrap.dedent("""
+            import threading
+            import _interpreters
+
+            def run(id):
+                _interpreters.exec(id, "import _datetime; print('a', end='')")
+                _interpreters.destroy(id)
+
+            ids = [_interpreters.create() for i in range(10)]
+            ts = [threading.Thread(target=run, args=(id,)) for id in ids]
+            for t in ts:
+                t.start()
+            for t in ts:
+                t.join()
+            """)
+        _, out, err = script_helper.assert_python_ok('-c', script)
+        self.assertEqual(out, b'a' * 10)
+        self.assertEqual(err, b'')
+
 
 def load_tests(loader, standard_tests, pattern):
     standard_tests.addTest(ZoneInfoCompleteTest())
diff --git a/Misc/NEWS.d/next/Library/2025-07-13-01-02-31.gh-issue-136421.5HKeoS.rst b/Misc/NEWS.d/next/Library/2025-07-13-01-02-31.gh-issue-136421.5HKeoS.rst
new file mode 100644
index 00000000000000..e61114f825a446
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-07-13-01-02-31.gh-issue-136421.5HKeoS.rst
@@ -0,0 +1,2 @@
+Fix crash in :mod:`datetime` when its static types are initialized or
+finalized by multiple interpreters concurrently.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 7a6426593d021f..07196ef0667b70 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -7335,12 +7335,17 @@ init_static_types(PyInterpreterState *interp, int reloading)
     if (reloading) {
         return 0;
     }
-
-    // `&...` is not a constant expression according to a strict reading
-    // of C standards. Fill tp_base at run-time rather than statically.
-    // See https://bugs.python.org/issue40777
-    PyDateTime_TimeZoneType.tp_base = &PyDateTime_TZInfoType;
-    PyDateTime_DateTimeType.tp_base = &PyDateTime_DateType;
+    if (_Py_IsMainInterpreter(interp)) {
+        if (PyType_HasFeature(&PyDateTime_DateType, Py_TPFLAGS_READY)) {
+            // This function was already called from PyInit__datetime()
+            return 0;
+        }
+        // `&...` is not a constant expression according to a strict reading
+        // of C standards. Fill tp_base at run-time rather than statically.
+        // See https://bugs.python.org/issue40777
+        PyDateTime_TimeZoneType.tp_base = &PyDateTime_TZInfoType;
+        PyDateTime_DateTimeType.tp_base = &PyDateTime_DateType;
+    }
 
     /* Bases classes must be initialized before subclasses,
      * so capi_types must have the types in the appropriate order. */
@@ -7564,6 +7569,13 @@ static PyModuleDef datetimemodule = {
 PyMODINIT_FUNC
 PyInit__datetime(void)
 {
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    // gh-136421: Ensure static types' runtime state gets cleared in shutting
+    // down the main interpreter rather than subinterpreters for concurrency.
+    assert(interp != NULL && _Py_IsMainInterpreter(interp));
+    if (init_static_types(interp, 0) < 0) {
+        return NULL;
+    }
     return PyModuleDef_Init(&datetimemodule);
 }