diff --git a/python/message.h b/python/message.h
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef PYPB_MESSAGE_H__
+#define PYPB_MESSAGE_H__
+
+#include <stdbool.h>
+
+#include "python/protobuf.h"
+#include "upb/reflection/message.h"
+
+// Removes the wrapper object for this field from the unset subobject cache.
+void PyUpb_Message_CacheDelete(PyObject* _self, const upb_FieldDef* f);
+
+// Sets the field value for `f` to `subobj`, evicting the wrapper object from
+// the "unset subobject" cache now that real data exists for it.  The caller
+// must also update the wrapper associated with `f` to point to `subobj` also.
+void PyUpb_Message_SetConcreteSubobj(PyObject* _self, const upb_FieldDef* f,
+                                     upb_MessageValue subobj);
+
+// Gets a Python wrapper object for message `u_msg` of type `m`, returning a
+// cached wrapper if one was previously created.  If a new object is created,
+// it will reference `arena`, which must own `u_msg`.
+PyObject* PyUpb_Message_Get(upb_Message* u_msg, const upb_MessageDef* m,
+                            PyObject* arena);
+
+// Verifies that a Python object is a message.  Sets a TypeError exception and
+// returns false on failure.
+bool PyUpb_Message_Verify(PyObject* self);
+
+// Gets the upb_Message* for this message object if the message is reified.
+// Otherwise returns NULL.
+upb_Message* PyUpb_Message_GetIfReified(PyObject* _self);
+
+// Returns the `upb_MessageDef` for a given Message.
+const upb_MessageDef* PyUpb_Message_GetMsgdef(PyObject* self);
+
+// Functions that match the corresponding methods on the message object.
+PyObject* PyUpb_Message_MergeFrom(PyObject* self, PyObject* arg);
+PyObject* PyUpb_Message_MergeFromString(PyObject* self, PyObject* arg);
+PyObject* PyUpb_Message_SerializeToString(PyObject* self, PyObject* args,
+                                          PyObject* kwargs);
+PyObject* PyUpb_Message_SerializePartialToString(PyObject* self, PyObject* args,
+                                                 PyObject* kwargs);
+
+// Sets fields of the message according to the attribuges in `kwargs`.
+int PyUpb_Message_InitAttributes(PyObject* _self, PyObject* args,
+                                 PyObject* kwargs);
+
+// Checks that `key` is a field descriptor for an extension type, and that the
+// extendee is this message.  Otherwise returns NULL and sets a KeyError.
+const upb_FieldDef* PyUpb_Message_GetExtensionDef(PyObject* _self,
+                                                  PyObject* key);
+
+// Clears the given field in this message.
+void PyUpb_Message_DoClearField(PyObject* _self, const upb_FieldDef* f);
+
+// Clears the ExtensionDict from the message.  The message must have an
+// ExtensionDict set.
+void PyUpb_Message_ClearExtensionDict(PyObject* _self);
+
+// Implements the equivalent of getattr(msg, field), once `field` has
+// already been resolved to a `upb_FieldDef*`.
+PyObject* PyUpb_Message_GetFieldValue(PyObject* _self,
+                                      const upb_FieldDef* field);
+
+// Implements the equivalent of setattr(msg, field, value), once `field` has
+// already been resolved to a `upb_FieldDef*`.
+int PyUpb_Message_SetFieldValue(PyObject* _self, const upb_FieldDef* field,
+                                PyObject* value, PyObject* exc);
+
+// Creates message meta class.
+PyObject* PyUpb_MessageMeta_DoCreateClass(PyObject* py_descriptor,
+                                          const char* name, PyObject* dict);
+
+// Returns the version associated with this message.  The version will be
+// incremented when the message changes.
+int PyUpb_Message_GetVersion(PyObject* _self);
+
+// Module-level init.
+bool PyUpb_InitMessage(PyObject* m);
+
+#endif  // PYPB_MESSAGE_H__