diff --git a/libs/checkpoint-postgres/uv.lock b/libs/checkpoint-postgres/uv.lock
index e6b1ad9ef..3b0643904 100644
--- a/libs/checkpoint-postgres/uv.lock
+++ b/libs/checkpoint-postgres/uv.lock
@@ -259,7 +259,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },
diff --git a/libs/checkpoint-sqlite/uv.lock b/libs/checkpoint-sqlite/uv.lock
index 894822b64..00ad52282 100644
--- a/libs/checkpoint-sqlite/uv.lock
+++ b/libs/checkpoint-sqlite/uv.lock
@@ -268,7 +268,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },
diff --git a/libs/checkpoint/langgraph/checkpoint/serde/event_hooks.py b/libs/checkpoint/langgraph/checkpoint/serde/event_hooks.py
new file mode 100644
index 000000000..9ea0a5b49
--- /dev/null
+++ b/libs/checkpoint/langgraph/checkpoint/serde/event_hooks.py
@@ -0,0 +1,52 @@
+from __future__ import annotations
+
+import logging
+from collections.abc import Callable
+from threading import Lock
+from typing import TypedDict
+
+from typing_extensions import NotRequired
+
+logger = logging.getLogger(__name__)
+
+
+class SerdeEvent(TypedDict):
+    kind: str
+    module: str
+    name: str
+    method: NotRequired[str]
+
+
+SerdeEventListener = Callable[[SerdeEvent], None]
+
+_listeners: list[SerdeEventListener] = []
+_listeners_lock = Lock()
+
+
+def register_serde_event_listener(listener: SerdeEventListener) -> Callable[[], None]:
+    """Register a listener for serde allowlist events."""
+    with _listeners_lock:
+        _listeners.append(listener)
+
+    def unregister() -> None:
+        with _listeners_lock:
+            try:
+                _listeners.remove(listener)
+            except ValueError:
+                pass
+
+    return unregister
+
+
+def emit_serde_event(event: SerdeEvent) -> None:
+    """Emit a serde event to all listeners.
+
+    Listener failures are isolated and logged.
+    """
+    with _listeners_lock:
+        listeners = tuple(_listeners)
+    for listener in listeners:
+        try:
+            listener(event)
+        except Exception:
+            logger.warning("Serde listener failed", exc_info=True)
diff --git a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
index e144303bc..4ef4a40b2 100644
--- a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
+++ b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
@@ -32,6 +32,7 @@ from langchain_core.load.load import Reviver
 
 from langgraph.checkpoint.serde import _msgpack as _lg_msgpack
 from langgraph.checkpoint.serde.base import SerializerProtocol
+from langgraph.checkpoint.serde.event_hooks import emit_serde_event
 from langgraph.checkpoint.serde.types import SendProtocol
 from langgraph.store.base import Item
 
@@ -519,6 +520,13 @@ def _create_msgpack_ext_hook(
 
         if allowed_modules is True:
             # default is to warn but allow unregistered types
+            emit_serde_event(
+                {
+                    "kind": "msgpack_unregistered_allowed",
+                    "module": module,
+                    "name": name,
+                }
+            )
             logger.warning(
                 "Deserializing unregistered type %s.%s from checkpoint. "
                 "This will be blocked in a future version. "
@@ -533,6 +541,13 @@ def _create_msgpack_ext_hook(
             if key in allowed_modules:
                 return True
         # strict mode blocks unregistered types
+        emit_serde_event(
+            {
+                "kind": "msgpack_blocked",
+                "module": module,
+                "name": name,
+            }
+        )
         logger.warning(
             "Blocked deserialization of %s.%s - not in allowed_msgpack_modules. "
             "Add to allowed_msgpack_modules to allow: [(%r, %r)]",
@@ -548,6 +563,14 @@ def _create_msgpack_ext_hook(
         key = (module, name, method)
         if key in _lg_msgpack.SAFE_MSGPACK_METHODS:
             return True
+        emit_serde_event(
+            {
+                "kind": "msgpack_method_blocked",
+                "module": module,
+                "name": name,
+                "method": method,
+            }
+        )
         logger.warning(
             "Blocked deserialization of method call %s.%s.%s - "
             "not in allowed methods set.",
diff --git a/libs/checkpoint/pyproject.toml b/libs/checkpoint/pyproject.toml
index 54c62ea73..1e51065d4 100644
--- a/libs/checkpoint/pyproject.toml
+++ b/libs/checkpoint/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 description = "Library with base interfaces for LangGraph checkpoint savers."
 authors = []
 requires-python = ">=3.10"
diff --git a/libs/checkpoint/tests/test_jsonplus.py b/libs/checkpoint/tests/test_jsonplus.py
index d153d3c7c..9242c59bf 100644
--- a/libs/checkpoint/tests/test_jsonplus.py
+++ b/libs/checkpoint/tests/test_jsonplus.py
@@ -25,6 +25,10 @@ from pydantic.v1 import SecretStr as SecretStrV1
 
 from langgraph.checkpoint.serde import _msgpack as _lg_msgpack
 from langgraph.checkpoint.serde._msgpack import AllowedMsgpackModules
+from langgraph.checkpoint.serde.event_hooks import (
+    SerdeEvent,
+    register_serde_event_listener,
+)
 from langgraph.checkpoint.serde.jsonplus import (
     EXT_METHOD_SINGLE_ARG,
     InvalidModuleError,
@@ -670,6 +674,40 @@ def test_msgpack_allowlist_blocks_non_listed(
     assert result == expected
 
 
+def test_msgpack_blocked_emits_event() -> None:
+    events: list[SerdeEvent] = []
+    unregister = register_serde_event_listener(events.append)
+    try:
+        serde = JsonPlusSerializer(allowed_msgpack_modules=None)
+        obj = AnotherPydantic(foo="nope")
+        serde.loads_typed(serde.dumps_typed(obj))
+    finally:
+        unregister()
+
+    assert {
+        "kind": "msgpack_blocked",
+        "module": "tests.test_jsonplus",
+        "name": "AnotherPydantic",
+    } in events
+
+
+def test_msgpack_unregistered_allowed_emits_event() -> None:
+    events: list[SerdeEvent] = []
+    unregister = register_serde_event_listener(events.append)
+    try:
+        serde = JsonPlusSerializer(allowed_msgpack_modules=True)
+        obj = AnotherPydantic(foo="ok")
+        serde.loads_typed(serde.dumps_typed(obj))
+    finally:
+        unregister()
+
+    assert {
+        "kind": "msgpack_unregistered_allowed",
+        "module": "tests.test_jsonplus",
+        "name": "AnotherPydantic",
+    } in events
+
+
 def test_msgpack_strict_allows_safe_types(
     caplog: pytest.LogCaptureFixture,
 ) -> None:
diff --git a/libs/checkpoint/uv.lock b/libs/checkpoint/uv.lock
index e80420d55..f95cf7a79 100644
--- a/libs/checkpoint/uv.lock
+++ b/libs/checkpoint/uv.lock
@@ -286,7 +286,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "." }
 dependencies = [
     { name = "langchain-core" },
diff --git a/libs/langgraph/uv.lock b/libs/langgraph/uv.lock
index 5c09be36d..75146458e 100644
--- a/libs/langgraph/uv.lock
+++ b/libs/langgraph/uv.lock
@@ -1548,7 +1548,7 @@ wheels = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },
diff --git a/libs/prebuilt/uv.lock b/libs/prebuilt/uv.lock
index 1f7cd6bb2..32c0ab357 100644
--- a/libs/prebuilt/uv.lock
+++ b/libs/prebuilt/uv.lock
@@ -352,7 +352,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },
diff --git a/libs/sdk-py/uv.lock b/libs/sdk-py/uv.lock
index 285f2738c..14f3b92c5 100644
--- a/libs/sdk-py/uv.lock
+++ b/libs/sdk-py/uv.lock
@@ -349,7 +349,7 @@ test = [
 
 [[package]]
 name = "langgraph-checkpoint"
-version = "4.0.1rc3"
+version = "4.0.1rc4"
 source = { editable = "../checkpoint" }
 dependencies = [
     { name = "langchain-core" },