diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5a1b7195..b60a1c4f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,9 +47,8 @@ jobs:
           python: "3.9"
         - ubuntu: "20.04"
           python: "3.10"
-        # 1 failing test: pickle_compatibility_test.py
-        # - ubuntu: "20.04"
-        #   python: "3.11"
+        - ubuntu: "20.04"
+          python: "3.11"
 
     name: "Ubuntu ${{ matrix.ubuntu }} - Python ${{ matrix.python }}"
     runs-on: ubuntu-latest
diff --git a/clif/pybind11/cindex/extractor.py b/clif/pybind11/cindex/extractor.py
index 0c6e9df1..0b9347e8 100644
--- a/clif/pybind11/cindex/extractor.py
+++ b/clif/pybind11/cindex/extractor.py
@@ -28,7 +28,7 @@ def _get_pointee_name(type_name: Text) -> Text:
   return type_name
 
 
-class Type(object):
+class Type:
   """Wraps a clang or a CLIF type."""
 
   def __init__(self, name: Text, is_pointer: bool, is_reference: bool,
@@ -115,7 +115,7 @@ def pointee_name(self):
       return ''
 
 
-class Function(object):
+class Function:
   """Wraps a clang or a CLIF Function."""
 
   def __init__(self, fq_name: Text, is_pure_virtual: bool,
@@ -191,7 +191,7 @@ def is_overloaded(self, is_overloaded: bool) -> None:
     self._is_overloaded = is_overloaded
 
 
-class Module(object):
+class Module:
   """Wraps a clang AST."""
 
   def __init__(self, tu: TranslationUnit):
diff --git a/clif/pybind11/function_lib.py b/clif/pybind11/function_lib.py
index 06c09ba3..b0534774 100644
--- a/clif/pybind11/function_lib.py
+++ b/clif/pybind11/function_lib.py
@@ -214,7 +214,7 @@ def generate_return_value_policy_for_type(
     for child_param_type in param_type.params:
       return_value_policy_list.append(
           generate_return_value_policy_for_type(
-              child_param_type, is_callable_arg
+              child_param_type, is_callable_arg, reference_internal
           )
       )
     return_value_policy_str = ', '.join(return_value_policy_list)
diff --git a/clif/pybind11/generator.py b/clif/pybind11/generator.py
index f8969797..9e68a2e3 100644
--- a/clif/pybind11/generator.py
+++ b/clif/pybind11/generator.py
@@ -43,7 +43,7 @@ def _generate_mangled_name_for_module(full_dotted_module_name: str) -> str:
   return full_dotted_module_name.replace('_', '__').replace('.', '_')
 
 
-class ModuleGenerator(object):
+class ModuleGenerator:
   """A class that generates pybind11 bindings code from CLIF ast."""
 
   def __init__(self, ast: ast_pb2.AST, module_path: str, header_path: str,
diff --git a/clif/pybind11/variables.py b/clif/pybind11/variables.py
index 3a6b5ac6..f80c9990 100644
--- a/clif/pybind11/variables.py
+++ b/clif/pybind11/variables.py
@@ -33,13 +33,20 @@ def _convert_ptr_to_ref(var_decl: ast_pb2.VarDecl) -> bool:
   )
 
 
-def _generate_self_param_with_type(
+def _generate_self_param_type(
     var_decl: ast_pb2.VarDecl,
     class_decl: ast_pb2.ClassDecl) -> str:
   if var_decl.is_extend_variable:
     assert var_decl.cpp_get.params
-    return f'{var_decl.cpp_get.params[0].cpp_exact_type} self'
-  return f'{class_decl.name.cpp_name} &self'
+    return var_decl.cpp_get.params[0].cpp_exact_type
+  return f'{class_decl.name.cpp_name}&'
+
+
+def _is_var_decl_type_cpp_copyable(var_decl: ast_pb2.VarDecl) -> bool:
+  if not var_decl.cpp_get.returns:
+    return var_decl.type.cpp_copyable
+  else:
+    return var_decl.cpp_get.returns[0].type.cpp_copyable
 
 
 def _generate_cpp_get(
@@ -65,11 +72,30 @@ def _generate_cpp_get(
   return_value_policy_pack = (
       f'py::return_value_policy_pack({return_value_policy})'
   )
-  self_param_with_type = _generate_self_param_with_type(var_decl, class_decl)
+
+  if not _is_var_decl_type_cpp_copyable(var_decl):
+    yield from _generate_cpp_get_for_uncopyable_type(
+        var_decl, class_decl, return_value_policy_pack, ret,
+        generate_comma=generate_comma)
+  else:
+    yield from _generate_cpp_get_for_copyable_type(
+        var_decl, class_decl, return_value_policy_pack, ret,
+        generate_comma=generate_comma)
+
+
+def _generate_cpp_get_for_copyable_type(
+    var_decl: ast_pb2.VarDecl,
+    class_decl: ast_pb2.ClassDecl,
+    return_value_policy_pack: str,
+    ret: str,
+    generate_comma: bool = False,
+) -> Generator[str, None, None]:
+  """Generate lambda expressions for getters when the type is copyable."""
+  self_param_type = _generate_self_param_type(var_decl, class_decl)
   if generate_comma:
-    yield I + f'py::cpp_function([]({self_param_with_type}) {{'
+    yield I + f'py::cpp_function([]({self_param_type} self) {{'
   else:
-    yield I + f'[]({self_param_with_type}) {{'
+    yield I + f'[]({self_param_type} self) {{'
   yield I + I + f'return {ret};'
   if generate_comma:
     yield I + f'}}, {return_value_policy_pack}),'
@@ -77,19 +103,49 @@ def _generate_cpp_get(
     yield I + f'}}, {return_value_policy_pack});'
 
 
+def _generate_cpp_get_for_uncopyable_type(
+    var_decl: ast_pb2.VarDecl,
+    class_decl: ast_pb2.ClassDecl,
+    return_value_policy_pack: str,
+    ret: str,
+    generate_comma: bool = False,
+) -> Generator[str, None, None]:
+  """Generate lambda expressions for getters when the type is uncopyable."""
+  if generate_comma:
+    yield I + 'py::cpp_function([](py::object self_py) -> py::object {'
+  else:
+    yield I + '[](py::object self_py) -> py::object {'
+  self_param_type = _generate_self_param_type(var_decl, class_decl)
+  yield I + I + f'{self_param_type} self = self_py.cast<{self_param_type}>();'
+  yield I + I + (f'return py::cast({ret}, {return_value_policy_pack}, '
+                 'self_py);')
+  if generate_comma:
+    yield I + '}),'
+  else:
+    yield I + '});'
+
+
 def _generate_cpp_set(
     var_decl: ast_pb2.VarDecl,
     class_decl: ast_pb2.ClassDecl,
+    generate_comma: bool = False,
 ) -> Generator[str, None, None]:
   """Generate lambda expressions for setters."""
-  yield I + (
-      f'[]({class_decl.name.cpp_name}& self, {var_decl.type.cpp_type} v) {{'
-  )
+  if generate_comma:
+    yield I + (f'py::cpp_function([]({class_decl.name.cpp_name}& self, '
+               f'{var_decl.type.cpp_type} v) {{')
+  else:
+    yield I + (
+        f'[]({class_decl.name.cpp_name}& self, {var_decl.type.cpp_type} v) {{'
+    )
   value = 'v'
   if var_decl.type.cpp_type.startswith('::std::unique_ptr'):
     value = 'std::move(v)'
   yield I + I + f'self.{var_decl.name.cpp_name} = {value};'
-  yield I + '});'
+  if generate_comma:
+    yield I + '}));'
+  else:
+    yield I + '});'
 
 
 def generate_from(
@@ -107,7 +163,7 @@ def generate_from(
     if _convert_ptr_to_ref(var_decl):
       yield f'{class_name}.def_property("{var_decl.name.native}", '
       yield from _generate_cpp_get(var_decl, class_decl, generate_comma=True)
-      yield from _generate_cpp_set(var_decl, class_decl)
+      yield from _generate_cpp_set(var_decl, class_decl, generate_comma=True)
     else:
       return_value_policy = function_lib.generate_return_value_policy_for_type(
           var_decl.type
diff --git a/clif/python/BUILD b/clif/python/BUILD
index 0c3e518a..ae1f876c 100644
--- a/clif/python/BUILD
+++ b/clif/python/BUILD
@@ -21,6 +21,7 @@ cc_library(
     hdrs = ["pickle_support.h"],
     visibility = ["//visibility:public"],
     deps = [
+        "@com_google_absl//absl/log:check",
         "@python_runtime//:python_headers",
     ],
 )
diff --git a/clif/python/clif_types.py b/clif/python/clif_types.py
index 1c0f0fae..3c90cc1f 100644
--- a/clif/python/clif_types.py
+++ b/clif/python/clif_types.py
@@ -42,7 +42,7 @@ def Namespace(typedef):
   return typedef.namespace or ''  # Collapse None -> ''.
 
 
-class TypeDef(object):
+class TypeDef:
   """C++ class as some Python object."""
   _genclifuse = False  # Generate '// CLIF use' in the header file.
 
diff --git a/clif/python/gen.py b/clif/python/gen.py
index ed892e86..5e492a39 100644
--- a/clif/python/gen.py
+++ b/clif/python/gen.py
@@ -163,7 +163,7 @@ def _DefTable(ctype, cname, lines):
   yield '};'
 
 
-class _MethodDef(object):
+class _MethodDef:
   name = 'MethodsStaticAlloc'
 
   def __call__(self, methods):
@@ -174,7 +174,7 @@ def __call__(self, methods):
 MethodDef = _MethodDef()  # pylint: disable=invalid-name
 
 
-class _GetSetDef(object):
+class _GetSetDef:
   # pylint: disable=missing-class-docstring
   name = 'Properties'
 
@@ -968,7 +968,7 @@ def CastAsCapsule(wrapped_cpp, pointer_name, wrapper):
   yield '}'
 
 
-class _NewIter(object):
+class _NewIter:
   """Generate the new_iter function."""
   name = 'new_iter'
 
@@ -986,7 +986,7 @@ def __call__(self, wrapped_iter, ns, wrapper, wrapper_type):
 NewIter = _NewIter()  # pylint: disable=invalid-name
 
 
-class _IterNext(object):
+class _IterNext:
   """Generate the iternext function."""
   name = 'iternext'
 
diff --git a/clif/python/pickle_support.cc b/clif/python/pickle_support.cc
index 81644ca5..224859e4 100644
--- a/clif/python/pickle_support.cc
+++ b/clif/python/pickle_support.cc
@@ -14,9 +14,44 @@
 
 #include <Python.h>
 
+#include "absl/log/check.h"
+
 namespace clif {
 
+namespace {
+
+#if PY_VERSION_HEX < 0x030B0000
+
+bool ClsGetStateIsBaseObjectGetstate(PyTypeObject*) { return false; }
+
+#else
+
+// The object.__getstate__() added with
+// https://github.com/python/cpython/pull/2821
+// is not suitable for extension types.
+bool ClsGetStateIsBaseObjectGetstate(PyTypeObject* cls) {
+  PyObject* base_getstate =
+      PyObject_GetAttrString((PyObject*)&PyBaseObject_Type, "__getstate__");
+  CHECK(base_getstate != nullptr);
+  PyObject* cls_getstate =
+      PyObject_GetAttrString((PyObject*)cls, "__getstate__");
+  if (cls_getstate == nullptr) {
+    PyErr_Clear();
+    Py_DECREF(base_getstate);
+    return false;
+  }
+  bool retval = (cls_getstate == base_getstate);
+  Py_DECREF(cls_getstate);
+  Py_DECREF(base_getstate);
+  return retval;
+}
+
+#endif
+
+}  // namespace
+
 PyObject* ReduceExCore(PyObject* self, const int protocol) {
+  PyTypeObject* cls = Py_TYPE(self);
   // Similar to time-tested approach used in Boost.Python:
   // https://www.boost.org/doc/libs/1_55_0/libs/python/doc/v2/pickle.html
   // https://github.com/boostorg/python/blob/develop/src/object/pickle_support.cpp
@@ -24,15 +59,17 @@ PyObject* ReduceExCore(PyObject* self, const int protocol) {
   if (getinitargs == nullptr) {
     PyErr_Clear();
   }
-  PyObject* getstate = PyObject_GetAttrString(self, "__getstate__");
-  if (getstate == nullptr) {
-    PyErr_Clear();
+  PyObject* getstate = nullptr;
+  if (!ClsGetStateIsBaseObjectGetstate(cls)) {
+    getstate = PyObject_GetAttrString(self, "__getstate__");
+    if (getstate == nullptr) {
+      PyErr_Clear();
+    }
   }
   PyObject* setstate = PyObject_GetAttrString(self, "__setstate__");
   if (setstate == nullptr) {
     PyErr_Clear();
   }
-  PyTypeObject* cls = Py_TYPE(self);
   PyObject* initargs_or_empty_tuple = nullptr;
   PyObject* empty_tuple = nullptr;
   PyObject* initargs = nullptr;
diff --git a/clif/python/primer.md b/clif/python/primer.md
index 35e769c3..13f7cbc7 100644
--- a/clif/python/primer.md
+++ b/clif/python/primer.md
@@ -131,7 +131,7 @@ Bar = ext.Bar
 
 
 @type_customization.extend(ext.Bar):
-class _(object):
+class _:
 
   def foo(self, ...):
     ...
diff --git a/clif/python/pyext.py b/clif/python/pyext.py
index 5d77041e..27416c16 100644
--- a/clif/python/pyext.py
+++ b/clif/python/pyext.py
@@ -94,8 +94,10 @@
 _ClassNamespace = lambda pyname: 'py' + pyname  # pylint: disable=invalid-name
 _ITER_KW = '__iter__'
 
+CLIF_MATCHER_VERSION_STAMP_REQUIRED_MINIMUM = 531560963
 
-class Context(object):
+
+class Context:
   """Reflection of C++ [nested] class/struct."""
   WRAPPER_CLASS_NAME = 'wrapper'
 
@@ -115,7 +117,7 @@ def _GetCppObj(get='cpp', py='self'):
   return 'reinterpret_cast<%s*>(%s)->%s' % (WRAPPER_CLASS_NAME, py, get)
 
 
-class Module(object):
+class Module:
   """Extended context for module namespace."""
 
   def __init__(self,
@@ -677,6 +679,17 @@ def GenInitFunction(self, api_source_h):
 
   def GenerateBase(self, ast, more_headers):
     """Extension module generation."""
+    if (
+        ast.clif_matcher_version_stamp is None
+        or ast.clif_matcher_version_stamp
+        < CLIF_MATCHER_VERSION_STAMP_REQUIRED_MINIMUM
+    ):
+      raise RuntimeError(
+          'Incompatible clif_matcher_version_stamp'
+          f' ("{ast.clif_matcher_argv0}"):'
+          f' {ast.clif_matcher_version_stamp} (required minimum:'
+          f' {CLIF_MATCHER_VERSION_STAMP_REQUIRED_MINIMUM})'
+      )
     ast_manipulations.MoveExtendsBackIntoClassesInPlace(ast)
     self.init += ast.extra_init
     for s in gen.Headlines(
diff --git a/clif/python/pytd2proto.py b/clif/python/pytd2proto.py
index 34e7cbd0..f0f6385f 100644
--- a/clif/python/pytd2proto.py
+++ b/clif/python/pytd2proto.py
@@ -101,7 +101,7 @@ def _read_include(input_stream, fname, prefix, typetable, capsules, interfaces,
       continue
 
 
-class Postprocessor(object):
+class Postprocessor:
   """Process parsed IR."""
 
   def __init__(self, config_headers=None, include_paths=('.',), preamble=''):
@@ -927,7 +927,7 @@ def set_func(self, pb, ast):
         _set_name(p.name, t.name)
 
 
-class _TypeTable(object):
+class _TypeTable:
   """Manage the Python -> C++ type name mappings.
 
   Normally, the Python -> C++ mapping is simple: replace '.' with '::'. However,
@@ -1150,7 +1150,7 @@ def __repr__(self):
     return '_TypeTable(types=\n{types}\n)'.format(types=types)
 
 
-class _TypeEntry(object):
+class _TypeEntry:
   """Type mapping information for use by _TypeTable.
 
   This is private to _TypeTable; _TypeTable has the public APIs for correctly
diff --git a/clif/python/type_customization.py b/clif/python/type_customization.py
index 9c374360..751c86a6 100644
--- a/clif/python/type_customization.py
+++ b/clif/python/type_customization.py
@@ -1,7 +1,7 @@
 """Decorator for adding attributes (incl. methods) into extension classes."""
 
 
-class _EmptyFromClass(object):
+class _EmptyFromClass:
   pass
 
 _EMPTY_FROM_CLASS_DICT_KEYS = frozenset(_EmptyFromClass.__dict__)
diff --git a/clif/testing/python/extend_methods_test.py b/clif/testing/python/extend_methods_test.py
index 61198e37..58de06c4 100644
--- a/clif/testing/python/extend_methods_test.py
+++ b/clif/testing/python/extend_methods_test.py
@@ -81,12 +81,12 @@ def a_property(self, value):
 
 
 @type_customization.extend(extend_methods.VirtualBaseHolder)
-class _(object):
+class _:
   """Added to VirtualBaseHolder."""
 
 
 @type_customization.extend(extend_methods.ConcreteHolder)
-class NamedFromClass(object):
+class NamedFromClass:
 
   def NfcInstanceMethod(self, prefix):
     return ':'.join(
@@ -109,7 +109,7 @@ def nfc_property(self, value):
     self.Set(value + 11)
 
 
-class NfcInstanceMethodOverride(object):
+class NfcInstanceMethodOverride:
 
   def NfcInstanceMethod(self, prefix):
     return ':'.join(
@@ -149,7 +149,7 @@ class _(_BaseOldStyleFailureTestBase, object):
   _base_old_style_failure_test_error = None
 
 
-class _BaseBaseFailureTestBase(object):
+class _BaseBaseFailureTestBase:
   pass
 
 
diff --git a/clif/testing/python/pickle_compatibility.py b/clif/testing/python/pickle_compatibility.py
index 909ccf6f..1b308533 100644
--- a/clif/testing/python/pickle_compatibility.py
+++ b/clif/testing/python/pickle_compatibility.py
@@ -19,7 +19,7 @@
 
 
 @type_customization.extend(StoreTwoUsingExtend)  # pylint: disable=undefined-variable
-class _(object):
+class _:
 
   def __reduce_ex__(self, protocol):
     return (self.__class__, (self.Get(0), self.Get(1)))
diff --git a/examples/extend_from_python/python/example.py b/examples/extend_from_python/python/example.py
index 8ee4a0a0..a082c906 100644
--- a/examples/extend_from_python/python/example.py
+++ b/examples/extend_from_python/python/example.py
@@ -26,7 +26,7 @@
 
 
 @type_customization.extend(ext.MyClass)
-class _(object):
+class _:
   """Anonymous helper class."""
 
   def g(self):