diff --git a/libs/core/langchain_core/utils/function_calling.py b/libs/core/langchain_core/utils/function_calling.py
index cda5569f795..7c91b84ee8a 100644
--- a/libs/core/langchain_core/utils/function_calling.py
+++ b/libs/core/langchain_core/utils/function_calling.py
@@ -508,6 +508,8 @@ _WellKnownOpenAITools = (
     "image_generation",
     "web_search_preview",
     "web_search",
+    "tool_search",
+    "namespace",
 )
 
 
diff --git a/libs/core/uv.lock b/libs/core/uv.lock
index 8dad83ef38f..612bb812126 100644
--- a/libs/core/uv.lock
+++ b/libs/core/uv.lock
@@ -992,7 +992,7 @@ wheels = [
 
 [[package]]
 name = "langchain-core"
-version = "1.2.16"
+version = "1.2.17"
 source = { editable = "." }
 dependencies = [
     { name = "jsonpatch" },
diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index 4351bd529b7..caa98740d5d 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -166,8 +166,15 @@ WellKnownTools = (
     "code_interpreter",
     "mcp",
     "image_generation",
+    "tool_search",
+    "namespace",
 )
 
+_OPENAI_EXTRA_FIELDS: set[str] = {
+    "defer_loading",
+}
+"""Valid OpenAI-specific extra fields that are promoted from BaseTool.extras."""
+
 
 def _convert_dict_to_message(_dict: Mapping[str, Any]) -> BaseMessage:
     """Convert a dictionary to a LangChain message.
@@ -1981,9 +1988,18 @@ class BaseChatOpenAI(BaseChatModel):
         """  # noqa: E501
         if parallel_tool_calls is not None:
             kwargs["parallel_tool_calls"] = parallel_tool_calls
-        formatted_tools = [
-            convert_to_openai_tool(tool, strict=strict) for tool in tools
-        ]
+        formatted_tools = []
+        for tool in tools:
+            formatted = convert_to_openai_tool(tool, strict=strict)
+            if (
+                isinstance(tool, BaseTool)
+                and hasattr(tool, "extras")
+                and isinstance(tool.extras, dict)
+            ):
+                for key, value in tool.extras.items():
+                    if key in _OPENAI_EXTRA_FIELDS:
+                        formatted[key] = value
+            formatted_tools.append(formatted)
         tool_names = []
         for tool in formatted_tools:
             if "function" in tool:
@@ -3981,7 +3997,11 @@ def _construct_responses_api_payload(
             # chat api: {"type": "function", "function": {"name": "...", "description": "...", "parameters": {...}, "strict": ...}}  # noqa: E501
             # responses api: {"type": "function", "name": "...", "description": "...", "parameters": {...}, "strict": ...}  # noqa: E501
             if tool["type"] == "function" and "function" in tool:
-                new_tools.append({"type": "function", **tool["function"]})
+                flattened = {"type": "function", **tool["function"]}
+                for key in _OPENAI_EXTRA_FIELDS:
+                    if key in tool:
+                        flattened[key] = tool[key]
+                new_tools.append(flattened)
             else:
                 if tool["type"] == "image_generation":
                     # Handle partial images (not yet supported)
diff --git a/libs/partners/openai/tests/integration_tests/chat_models/test_responses_api.py b/libs/partners/openai/tests/integration_tests/chat_models/test_responses_api.py
index 56c9e4595f7..052f3e8ba3c 100644
--- a/libs/partners/openai/tests/integration_tests/chat_models/test_responses_api.py
+++ b/libs/partners/openai/tests/integration_tests/chat_models/test_responses_api.py
@@ -1267,3 +1267,60 @@ def test_csv_input() -> None:
         "3" in str(response2.content).lower()
         or "three" in str(response2.content).lower()
     )
+
+
+def test_tool_search() -> None:
+    """Test tool search with defer_loading via extras on BaseTool."""
+    from langchain_core.tools import tool
+
+    @tool(extras={"defer_loading": True})
+    def get_weather(location: str) -> str:
+        """Get the current weather for a location."""
+        return f"Sunny in {location}"
+
+    @tool(extras={"defer_loading": True})
+    def get_population(city: str) -> str:
+        """Get the population of a city."""
+        return f"Population of {city}: 1,000,000"
+
+    llm = ChatOpenAI(model="gpt-4.1-mini")
+    bound = llm.bind_tools(
+        [get_weather, get_population, {"type": "tool_search"}],
+        parallel_tool_calls=False,
+    )
+    response = cast(AIMessage, bound.invoke("What's the weather in San Francisco?"))
+    assert response.tool_calls
+    assert response.tool_calls[0]["name"] == "get_weather"
+
+
+def test_tool_search_with_namespace() -> None:
+    """Test tool search with namespace and defer_loading."""
+    weather_ns = {
+        "type": "namespace",
+        "name": "weather",
+        "description": "Weather tools for looking up current conditions.",
+        "tools": [
+            {
+                "type": "function",
+                "name": "get_weather",
+                "description": "Get the current weather for a location.",
+                "defer_loading": True,
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "location": {"type": "string"},
+                    },
+                    "required": ["location"],
+                    "additionalProperties": False,
+                },
+            }
+        ],
+    }
+    llm = ChatOpenAI(model="gpt-4.1-mini")
+    bound = llm.bind_tools(
+        [weather_ns, {"type": "tool_search"}],
+        parallel_tool_calls=False,
+    )
+    response = cast(AIMessage, bound.invoke("What's the weather in San Francisco?"))
+    assert response.tool_calls
+    assert response.tool_calls[0]["name"] == "get_weather"
diff --git a/libs/partners/openai/tests/unit_tests/test_tools.py b/libs/partners/openai/tests/unit_tests/test_tools.py
index 07a3b86d412..eabd95ff36f 100644
--- a/libs/partners/openai/tests/unit_tests/test_tools.py
+++ b/libs/partners/openai/tests/unit_tests/test_tools.py
@@ -1,5 +1,5 @@
 from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
-from langchain_core.tools import Tool
+from langchain_core.tools import Tool, tool
 
 from langchain_openai import ChatOpenAI, custom_tool
 
@@ -96,6 +96,70 @@ def test_custom_tool() -> None:
     assert payload["input"] == expected_input
 
 
+def test_extras_with_defer_loading() -> None:
+    @tool(extras={"defer_loading": True})
+    def get_weather(location: str) -> str:
+        """Get the current weather for a location."""
+        return f"Sunny in {location}"
+
+    llm = ChatOpenAI(model="gpt-4.1", use_responses_api=True)
+    bound = llm.bind_tools(
+        [get_weather, {"type": "tool_search"}],
+    )
+    tools = bound.kwargs["tools"]  # type: ignore[attr-defined]
+    func_tool = next(t for t in tools if t["type"] == "function")
+    assert func_tool["defer_loading"] is True
+    assert func_tool["function"]["name"] == "get_weather"
+    assert any(t["type"] == "tool_search" for t in tools)
+
+    from langchain_openai.chat_models.base import _construct_responses_api_payload
+
+    payload = _construct_responses_api_payload(
+        [HumanMessage("hello")],
+        {"model": "gpt-4.1", "stream": False, "tools": list(tools)},
+    )
+    resp_tools = payload["tools"]
+    resp_func = next(t for t in resp_tools if t["type"] == "function")
+    assert resp_func["defer_loading"] is True
+    assert resp_func["name"] == "get_weather"
+    assert any(t["type"] == "tool_search" for t in resp_tools)
+
+
+def test_tool_search_dict_passthrough() -> None:
+    llm = ChatOpenAI(model="gpt-4.1", use_responses_api=True)
+    tool_search = {"type": "tool_search"}
+    bound = llm.bind_tools([tool_search])
+    tools = bound.kwargs["tools"]  # type: ignore[attr-defined]
+    assert any(t["type"] == "tool_search" for t in tools)
+
+
+def test_namespace_dict_passthrough() -> None:
+    llm = ChatOpenAI(model="gpt-4.1", use_responses_api=True)
+    ns = {
+        "type": "namespace",
+        "name": "crm",
+        "description": "CRM tools.",
+        "tools": [
+            {
+                "type": "function",
+                "name": "list_orders",
+                "description": "List orders.",
+                "defer_loading": True,
+                "parameters": {
+                    "type": "object",
+                    "properties": {"customer_id": {"type": "string"}},
+                    "required": ["customer_id"],
+                    "additionalProperties": False,
+                },
+            }
+        ],
+    }
+    bound = llm.bind_tools([ns, {"type": "tool_search"}])
+    tools = bound.kwargs["tools"]  # type: ignore[attr-defined]
+    assert any(t["type"] == "namespace" for t in tools)
+    assert any(t["type"] == "tool_search" for t in tools)
+
+
 async def test_async_custom_tool() -> None:
     @custom_tool
     async def my_async_tool(x: str) -> str:
diff --git a/libs/partners/openai/uv.lock b/libs/partners/openai/uv.lock
index 83c3081a9bb..64e24ead33b 100644
--- a/libs/partners/openai/uv.lock
+++ b/libs/partners/openai/uv.lock
@@ -610,7 +610,7 @@ typing = [
 
 [[package]]
 name = "langchain-core"
-version = "1.2.16"
+version = "1.2.17"
 source = { editable = "../../core" }
 dependencies = [
     { name = "jsonpatch" },