diff --git a/libs/sdk-py/langgraph_sdk/_async/cron.py b/libs/sdk-py/langgraph_sdk/_async/cron.py
index 792fba5b0..824b86f55 100644
--- a/libs/sdk-py/langgraph_sdk/_async/cron.py
+++ b/libs/sdk-py/langgraph_sdk/_async/cron.py
@@ -8,7 +8,11 @@ from datetime import datetime, tzinfo
 from typing import Any
 
 from langgraph_sdk._async.http import HttpClient
-from langgraph_sdk._shared.utilities import _quote_path_param, _resolve_timezone
+from langgraph_sdk._shared.utilities import (
+    NOT_PROVIDED,
+    _quote_path_param,
+    _resolve_timezone,
+)
 from langgraph_sdk.schema import (
     All,
     Config,
@@ -324,7 +328,7 @@ class CronClient:
         cron_id: str,
         *,
         schedule: str | None = None,
-        end_time: datetime | None = None,
+        end_time: datetime | None = NOT_PROVIDED,
         input: Input | None = None,
         metadata: Mapping[str, Any] | None = None,
         config: Config | None = None,
@@ -348,7 +352,8 @@ class CronClient:
             cron_id: The cron ID to update.
             schedule: The cron schedule to execute this job on.
                 Schedules are interpreted in UTC unless a timezone is specified.
-            end_time: The end date to stop running the cron.
+            end_time: The end date to stop running the cron. Pass ``None`` to
+                clear a previously set end time; omit to leave it unchanged.
             input: The input to the graph.
             metadata: Metadata to assign to the cron job runs.
             config: The configuration for the assistant.
@@ -386,7 +391,6 @@ class CronClient:
         """
         payload = {
             "schedule": schedule,
-            "end_time": end_time.isoformat() if end_time else None,
             "input": input,
             "metadata": metadata,
             "config": config,
@@ -403,6 +407,10 @@ class CronClient:
             "durability": durability,
         }
         payload = {k: v for k, v in payload.items() if v is not None}
+        # An explicit end_time=None clears the end time; NOT_PROVIDED leaves it
+        # unchanged. Inject after the None-strip so the explicit null survives.
+        if end_time is not NOT_PROVIDED:
+            payload["end_time"] = end_time.isoformat() if end_time is not None else None
         return await self.http.patch(
             f"/runs/crons/{_quote_path_param(cron_id)}",
             json=payload,
diff --git a/libs/sdk-py/langgraph_sdk/_sync/cron.py b/libs/sdk-py/langgraph_sdk/_sync/cron.py
index 24acae5bd..464edb80d 100644
--- a/libs/sdk-py/langgraph_sdk/_sync/cron.py
+++ b/libs/sdk-py/langgraph_sdk/_sync/cron.py
@@ -7,7 +7,11 @@ from collections.abc import Mapping, Sequence
 from datetime import datetime, tzinfo
 from typing import Any
 
-from langgraph_sdk._shared.utilities import _quote_path_param, _resolve_timezone
+from langgraph_sdk._shared.utilities import (
+    NOT_PROVIDED,
+    _quote_path_param,
+    _resolve_timezone,
+)
 from langgraph_sdk._sync.http import SyncHttpClient
 from langgraph_sdk.schema import (
     All,
@@ -313,7 +317,7 @@ class SyncCronClient:
         cron_id: str,
         *,
         schedule: str | None = None,
-        end_time: datetime | None = None,
+        end_time: datetime | None = NOT_PROVIDED,
         input: Input | None = None,
         metadata: Mapping[str, Any] | None = None,
         config: Config | None = None,
@@ -337,7 +341,8 @@ class SyncCronClient:
             cron_id: The cron ID to update.
             schedule: The cron schedule to execute this job on.
                 Schedules are interpreted in UTC unless a timezone is specified.
-            end_time: The end date to stop running the cron.
+            end_time: The end date to stop running the cron. Pass ``None`` to
+                clear a previously set end time; omit to leave it unchanged.
             input: The input to the graph.
             metadata: Metadata to assign to the cron job runs.
             config: The configuration for the assistant.
@@ -375,7 +380,6 @@ class SyncCronClient:
         """
         payload = {
             "schedule": schedule,
-            "end_time": end_time.isoformat() if end_time else None,
             "input": input,
             "metadata": metadata,
             "config": config,
@@ -392,6 +396,10 @@ class SyncCronClient:
             "durability": durability,
         }
         payload = {k: v for k, v in payload.items() if v is not None}
+        # An explicit end_time=None clears the end time; NOT_PROVIDED leaves it
+        # unchanged. Inject after the None-strip so the explicit null survives.
+        if end_time is not NOT_PROVIDED:
+            payload["end_time"] = end_time.isoformat() if end_time is not None else None
         return self.http.patch(
             f"/runs/crons/{_quote_path_param(cron_id)}",
             json=payload,
diff --git a/libs/sdk-py/tests/test_crons_client.py b/libs/sdk-py/tests/test_crons_client.py
index 122dda638..7e38e25f1 100644
--- a/libs/sdk-py/tests/test_crons_client.py
+++ b/libs/sdk-py/tests/test_crons_client.py
@@ -396,6 +396,32 @@ async def test_async_update_with_end_time():
     assert result == cron
 
 
+@pytest.mark.asyncio
+async def test_async_update_clears_end_time():
+    """Test that CronClient.update sends an explicit null end_time to clear it."""
+    cron = _cron_response()
+
+    async def handler(request: httpx.Request) -> httpx.Response:
+        assert request.method == "PATCH"
+        assert request.url.path == "/runs/crons/cron_123"
+
+        body = json.loads(request.content)
+        assert "end_time" in body  # Explicit None must survive the None-strip
+        assert body["end_time"] is None
+
+        return httpx.Response(200, json=cron)
+
+    transport = httpx.MockTransport(handler)
+    async with httpx.AsyncClient(
+        transport=transport, base_url="https://example.com"
+    ) as client:
+        http_client = HttpClient(client)
+        cron_client = CronClient(http_client)
+        result = await cron_client.update(cron_id="cron_123", end_time=None)
+
+    assert result == cron
+
+
 def test_sync_update():
     """Test that SyncCronClient.update works with schedule and enabled parameters."""
     cron = _cron_response()
@@ -456,6 +482,29 @@ def test_sync_update_with_end_time():
     assert result == cron
 
 
+def test_sync_update_clears_end_time():
+    """Test that SyncCronClient.update sends an explicit null end_time to clear it."""
+    cron = _cron_response()
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        assert request.method == "PATCH"
+        assert request.url.path == "/runs/crons/cron_123"
+
+        body = json.loads(request.content)
+        assert "end_time" in body  # Explicit None must survive the None-strip
+        assert body["end_time"] is None
+
+        return httpx.Response(200, json=cron)
+
+    transport = httpx.MockTransport(handler)
+    with httpx.Client(transport=transport, base_url="https://example.com") as client:
+        http_client = SyncHttpClient(client)
+        cron_client = SyncCronClient(http_client)
+        result = cron_client.update(cron_id="cron_123", end_time=None)
+
+    assert result == cron
+
+
 @pytest.mark.parametrize(
     "enabled_value",
     [True, False],