diff --git a/packages/toolbox-langchain/src/toolbox_langchain/async_client.py b/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
index f622b65f0..d94d25b2a 100644
--- a/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
+++ b/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
@@ -17,6 +17,7 @@
 
 from aiohttp import ClientSession
 from toolbox_core.client import ToolboxClient as ToolboxCoreClient
+from toolbox_core.protocol import Protocol
 
 from .async_tools import AsyncToolboxTool
 
@@ -33,6 +34,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
+        protocol: Protocol = Protocol.MCP,
     ):
         """
         Initializes the AsyncToolboxClient for the Toolbox service at the given URL.
@@ -42,7 +44,7 @@ def __init__(
             session: An HTTP client session.
         """
         self.__core_client = ToolboxCoreClient(
-            url=url, session=session, client_headers=client_headers
+            url=url, session=session, client_headers=client_headers, protocol=protocol
         )
 
     async def aload_tool(
diff --git a/packages/toolbox-langchain/src/toolbox_langchain/client.py b/packages/toolbox-langchain/src/toolbox_langchain/client.py
index e8c87b241..a93d1ec6d 100644
--- a/packages/toolbox-langchain/src/toolbox_langchain/client.py
+++ b/packages/toolbox-langchain/src/toolbox_langchain/client.py
@@ -16,6 +16,7 @@
 from typing import Any, Awaitable, Callable, Mapping, Optional, Union
 from warnings import warn
 
+from toolbox_core.protocol import Protocol
 from toolbox_core.sync_client import ToolboxSyncClient as ToolboxCoreSyncClient
 
 from .tools import ToolboxTool
@@ -29,6 +30,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
+        protocol: Protocol = Protocol.MCP,
     ) -> None:
         """
         Initializes the ToolboxClient for the Toolbox service at the given URL.
@@ -37,7 +39,7 @@ def __init__(
             url: The base URL of the Toolbox service.
         """
         self.__core_client = ToolboxCoreSyncClient(
-            url=url, client_headers=client_headers
+            url=url, client_headers=client_headers, protocol=protocol
         )
 
     async def aload_tool(
diff --git a/packages/toolbox-langchain/tests/test_async_client.py b/packages/toolbox-langchain/tests/test_async_client.py
index a0c9def58..ced88bbaa 100644
--- a/packages/toolbox-langchain/tests/test_async_client.py
+++ b/packages/toolbox-langchain/tests/test_async_client.py
@@ -19,6 +19,7 @@
 from aiohttp import ClientSession
 from toolbox_core.client import ToolboxClient as ToolboxCoreClient
 from toolbox_core.protocol import ParameterSchema as CoreParameterSchema
+from toolbox_core.protocol import Protocol
 from toolbox_core.tool import ToolboxTool as ToolboxCoreTool
 
 from toolbox_langchain.async_client import AsyncToolboxClient
@@ -348,5 +349,8 @@ async def test_init_with_client_headers(
         headers = {"X-Test-Header": "value"}
         AsyncToolboxClient(URL, session=mock_session, client_headers=headers)
         mock_core_client_constructor.assert_called_once_with(
-            url=URL, session=mock_session, client_headers=headers
+            url=URL,
+            session=mock_session,
+            client_headers=headers,
+            protocol=Protocol.MCP_v20250618,
         )
diff --git a/packages/toolbox-langchain/tests/test_client.py b/packages/toolbox-langchain/tests/test_client.py
index da9dfcecf..4ec8d52e2 100644
--- a/packages/toolbox-langchain/tests/test_client.py
+++ b/packages/toolbox-langchain/tests/test_client.py
@@ -17,6 +17,7 @@
 import pytest
 from pydantic import BaseModel
 from toolbox_core.protocol import ParameterSchema as CoreParameterSchema
+from toolbox_core.protocol import Protocol
 from toolbox_core.sync_tool import ToolboxSyncTool as ToolboxCoreSyncTool
 from toolbox_core.utils import params_to_pydantic_model
 
@@ -490,7 +491,7 @@ def test_init_with_client_headers(self, mock_core_client_constructor):
         headers = {"X-Test-Header": "value"}
         ToolboxClient(URL, client_headers=headers)
         mock_core_client_constructor.assert_called_once_with(
-            url=URL, client_headers=headers
+            url=URL, client_headers=headers, protocol=Protocol.MCP_v20250618
         )
 
     @patch("toolbox_langchain.client.ToolboxCoreSyncClient")