diff --git a/source/cbor.c b/source/cbor.c
index 602ccb21d..8cc9f76cb 100644
--- a/source/cbor.c
+++ b/source/cbor.c
@@ -183,30 +183,68 @@ static PyObject *s_cbor_encoder_write_pyobject(struct aws_cbor_encoder *encoder,
     /**
      * TODO: timestamp <-> datetime?? Decimal fraction <-> decimal??
      */
-    if (PyLong_CheckExact(py_object)) {
-        return s_cbor_encoder_write_pylong(encoder, py_object);
-    } else if (PyFloat_CheckExact(py_object)) {
-        return s_cbor_encoder_write_pyobject_as_float(encoder, py_object);
-    } else if (PyBool_Check(py_object)) {
-        return s_cbor_encoder_write_pyobject_as_bool(encoder, py_object);
-    } else if (PyBytes_CheckExact(py_object)) {
-        return s_cbor_encoder_write_pyobject_as_bytes(encoder, py_object);
-    } else if (PyUnicode_Check(py_object)) {
+
+    /* Handle None first as it's a singleton, not a type */
+    if (py_object == Py_None) {
+        aws_cbor_encoder_write_null(encoder);
+        Py_RETURN_NONE;
+    }
+
+    /* Get type once for efficiency - PyObject_Type returns a new reference */
+    /* https://docs.python.org/3/c-api/structures.html#c.Py_TYPE is not a stable API until 3.14, so that we cannot use
+     * it. */
+    PyObject *type = PyObject_Type(py_object);
+    if (!type) {
+        return NULL;
+    }
+
+    PyObject *result = NULL;
+
+    /* Exact type matches first (no subclasses) - fast path */
+    if (type == (PyObject *)&PyLong_Type) {
+        result = s_cbor_encoder_write_pylong(encoder, py_object);
+    } else if (type == (PyObject *)&PyFloat_Type) {
+        result = s_cbor_encoder_write_pyobject_as_float(encoder, py_object);
+    } else if (type == (PyObject *)&PyBool_Type) {
+        result = s_cbor_encoder_write_pyobject_as_bool(encoder, py_object);
+    } else if (type == (PyObject *)&PyBytes_Type) {
+        result = s_cbor_encoder_write_pyobject_as_bytes(encoder, py_object);
+    } else if (PyType_IsSubtype((PyTypeObject *)type, &PyUnicode_Type)) {
         /* Allow subclasses of `str` */
-        return s_cbor_encoder_write_pyobject_as_text(encoder, py_object);
-    } else if (PyList_Check(py_object)) {
+        result = s_cbor_encoder_write_pyobject_as_text(encoder, py_object);
+    } else if (PyType_IsSubtype((PyTypeObject *)type, &PyList_Type)) {
         /* Write py_list, allow subclasses of `list` */
-        return s_cbor_encoder_write_pylist(encoder, py_object);
-    } else if (PyDict_Check(py_object)) {
+        result = s_cbor_encoder_write_pylist(encoder, py_object);
+    } else if (PyType_IsSubtype((PyTypeObject *)type, &PyDict_Type)) {
         /* Write py_dict, allow subclasses of `dict` */
-        return s_cbor_encoder_write_pydict(encoder, py_object);
-    } else if (py_object == Py_None) {
-        aws_cbor_encoder_write_null(encoder);
+        result = s_cbor_encoder_write_pydict(encoder, py_object);
     } else {
-        PyErr_Format(PyExc_ValueError, "Not supported type %R", (PyObject *)Py_TYPE(py_object));
+        /* Check for datetime using stable ABI (slower, so checked last) */
+        bool is_datetime = false;
+        if (aws_py_is_datetime_instance(py_object, &is_datetime) != AWS_OP_SUCCESS) {
+            /* Error occurred during datetime check */
+            result = NULL;
+        } else if (is_datetime) {
+            /* Convert datetime to CBOR epoch time (tag 1) */
+            /* Call timestamp() method - PyObject_CallMethod is more idiomatic and compatible with Python 3.8+ */
+            PyObject *timestamp = PyObject_CallMethod(py_object, "timestamp", NULL);
+            if (timestamp) {
+                /* Write CBOR tag 1 (epoch time) + timestamp */
+                aws_cbor_encoder_write_tag(encoder, AWS_CBOR_TAG_EPOCH_TIME);
+                result = s_cbor_encoder_write_pyobject_as_float(encoder, timestamp);
+                Py_DECREF(timestamp);
+            } else {
+                result = NULL; /* timestamp() call failed */
+            }
+        } else {
+            /* Unsupported type */
+            PyErr_Format(PyExc_ValueError, "Not supported type %R", type);
+        }
     }
 
-    Py_RETURN_NONE;
+    /* Release the type reference */
+    Py_DECREF(type);
+    return result;
 }
 
 /*********************************** BINDINGS ***********************************************/
diff --git a/source/module.c b/source/module.c
index 6da50b3d8..356be886f 100644
--- a/source/module.c
+++ b/source/module.c
@@ -36,6 +36,51 @@
 static struct aws_logger s_logger;
 static bool s_logger_init = false;
 
+/*******************************************************************************
+ * DateTime Type Cache (for stable ABI compatibility)
+ ******************************************************************************/
+static PyObject *s_datetime_class = NULL;
+
+static int s_init_datetime_cache(void) {
+    if (s_datetime_class) {
+        return AWS_OP_SUCCESS; /* Already initialized */
+    }
+
+    /* Import datetime module */
+    PyObject *datetime_module = PyImport_ImportModule("datetime");
+    if (!datetime_module) {
+        /* Python exception already set by PyImport_ImportModule */
+        return aws_py_raise_error();
+    }
+
+    /* Get datetime class - new reference we'll keep */
+    s_datetime_class = PyObject_GetAttrString(datetime_module, "datetime");
+    Py_DECREF(datetime_module);
+
+    if (!s_datetime_class) {
+        /* Python exception already set by PyObject_GetAttrString */
+        return aws_py_raise_error();
+    }
+
+    return AWS_OP_SUCCESS;
+}
+
+int aws_py_is_datetime_instance(PyObject *obj, bool *out_is_datetime) {
+    AWS_ASSERT(out_is_datetime);
+
+    if (!s_datetime_class && s_init_datetime_cache() != AWS_OP_SUCCESS) {
+        return AWS_OP_ERR;
+    }
+
+    int result = PyObject_IsInstance(obj, s_datetime_class);
+    if (result < 0) {
+        return aws_py_raise_error(); /* PyObject_IsInstance failed */
+    }
+
+    *out_is_datetime = (result != 0);
+    return AWS_OP_SUCCESS;
+}
+
 PyObject *aws_py_init_logging(PyObject *self, PyObject *args) {
     (void)self;
 
@@ -1035,6 +1080,12 @@ PyMODINIT_FUNC PyInit__awscrt(void) {
     aws_register_error_info(&s_error_list);
     s_error_map_init();
 
+    /* Initialize datetime type cache for stable ABI datetime support */
+    if (s_init_datetime_cache() < 0) {
+        /* Non-fatal: datetime encoding will fail but rest of module works */
+        PyErr_Clear();
+    }
+
     return m;
 }
 
diff --git a/source/module.h b/source/module.h
index 2f9dd217e..52d9165d7 100644
--- a/source/module.h
+++ b/source/module.h
@@ -70,6 +70,15 @@ struct aws_byte_cursor aws_byte_cursor_from_pyunicode(PyObject *str);
  * If conversion cannot occur, cursor->ptr will be NULL and a python exception is set */
 struct aws_byte_cursor aws_byte_cursor_from_pybytes(PyObject *py_bytes);
 
+/**
+ * Check if a PyObject is an instance of datetime.datetime using stable ABI.
+ *
+ * @param obj PyObject to check
+ * @param out_is_datetime Pointer to store result (true if datetime, false otherwise)
+ * @return AWS_OP_SUCCESS on success, AWS_OP_ERR on error (Python exception set)
+ */
+int aws_py_is_datetime_instance(PyObject *obj, bool *out_is_datetime);
+
 /* Set current thread's error indicator based on aws_last_error() */
 void PyErr_SetAwsLastError(void);
 
diff --git a/test/test_cbor.py b/test/test_cbor.py
index 3ab65b569..df055ea25 100644
--- a/test/test_cbor.py
+++ b/test/test_cbor.py
@@ -151,6 +151,86 @@ def on_epoch_time(epoch_secs):
             exception = e
         self.assertIsNotNone(exception)
 
+    def test_cbor_encode_decode_datetime(self):
+        """Test automatic datetime encoding/decoding"""
+        # Create a datetime object
+        dt = datetime.datetime(2024, 1, 1, 12, 0, 0)
+
+        # Encode datetime - should automatically convert to CBOR tag 1 + timestamp
+        encoder = AwsCborEncoder()
+        encoder.write_data_item(dt)
+
+        # Decode with callback to convert back to datetime
+        def on_epoch_time(epoch_secs):
+            return datetime.datetime.fromtimestamp(epoch_secs)
+
+        decoder = AwsCborDecoder(encoder.get_encoded_data(), on_epoch_time)
+        result = decoder.pop_next_data_item()
+
+        # Verify the result matches original datetime
+        self.assertEqual(dt, result)
+        self.assertIsInstance(result, datetime.datetime)
+
+        # Test datetime with microsecond precision (milliseconds)
+        dt_with_microseconds = datetime.datetime(2024, 1, 1, 12, 0, 0, 123456)  # 123.456 milliseconds
+        encoder3 = AwsCborEncoder()
+        encoder3.write_data_item(dt_with_microseconds)
+
+        decoder3 = AwsCborDecoder(encoder3.get_encoded_data(), on_epoch_time)
+        result_microseconds = decoder3.pop_next_data_item()
+
+        # Verify microsecond precision is preserved
+        self.assertEqual(dt_with_microseconds, result_microseconds)
+        self.assertEqual(dt_with_microseconds.microsecond, result_microseconds.microsecond)
+        self.assertIsInstance(result_microseconds, datetime.datetime)
+
+        # Test datetime in a list
+        encoder2 = AwsCborEncoder()
+        test_list = [dt, "text", 123, dt_with_microseconds]
+        encoder2.write_data_item(test_list)
+
+        decoder2 = AwsCborDecoder(encoder2.get_encoded_data(), on_epoch_time)
+        result_list = decoder2.pop_next_data_item()
+
+        self.assertEqual(len(result_list), 4)
+        self.assertEqual(result_list[0], dt)
+        self.assertEqual(result_list[1], "text")
+        self.assertEqual(result_list[2], 123)
+        self.assertEqual(result_list[3], dt_with_microseconds)
+        # Verify microsecond precision in list
+        self.assertEqual(result_list[3].microsecond, 123456)
+
+    def test_cbor_encode_unsupported_type(self):
+        """Test that encoding unsupported types raises ValueError"""
+        # Create a custom class that's not supported by CBOR encoder
+        class CustomClass:
+            def __init__(self, value):
+                self.value = value
+
+        # Try to encode an unsupported type
+        encoder = AwsCborEncoder()
+        unsupported_obj = CustomClass(42)
+
+        # Should raise ValueError with message about unsupported type
+        with self.assertRaises(ValueError) as context:
+            encoder.write_data_item(unsupported_obj)
+        # Verify the error message mentions "Not supported type"
+        self.assertIn("Not supported type", str(context.exception))
+
+        # Test unsupported type in a list (should also fail)
+        encoder2 = AwsCborEncoder()
+        with self.assertRaises(ValueError) as context2:
+            encoder2.write_data_item([1, 2, unsupported_obj, 3])
+
+        self.assertIn("Not supported type", str(context2.exception))
+
+        # Test unsupported type as dict key (should also fail)
+        encoder3 = AwsCborEncoder()
+        with self.assertRaises(ValueError) as context3:
+            encoder3.write_data_item({unsupported_obj: "value"})
+
+        self.assertIn("Not supported type", str(context3.exception))
+
     def _ieee754_bits_to_float(self, bits):
         return struct.unpack('>f', struct.pack('>I', bits))[0]