From ef360465485bd4178859f9a2650300cf9b4b3610 Mon Sep 17 00:00:00 2001
From: Mahmut CAVDAR <4072246+mcavdar@users.noreply.github.com>
Date: Mon, 27 Oct 2025 12:05:17 +0100
Subject: [PATCH 1/2] Replace ModelRequestHandler with Callable[[ModelRequest],
 ModelResponse]

---
 src/oss/python/migrate/langchain-v1.mdx | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/oss/python/migrate/langchain-v1.mdx b/src/oss/python/migrate/langchain-v1.mdx
index 4b4191c7a..ec3c70933 100644
--- a/src/oss/python/migrate/langchain-v1.mdx
+++ b/src/oss/python/migrate/langchain-v1.mdx
@@ -492,24 +492,24 @@ This functionality has been ported to the middleware interface in v1.
 ```python v1 (new)
 from langchain.agents import create_agent
 from langchain.agents.middleware import (
-    AgentMiddleware, ModelRequest, ModelRequestHandler
+    AgentMiddleware, ModelRequest
 )
-from langchain.messages import AIMessage
+from langchain.agents.middleware.types import ModelResponse
 from langchain_openai import ChatOpenAI
-
+from typing import Callable
 
 basic_model = ChatOpenAI(model="gpt-5-nano")
 advanced_model = ChatOpenAI(model="gpt-5")
 
 class DynamicModelMiddleware(AgentMiddleware):
 
-    def wrap_model_call(self, request: ModelRequest, handler: ModelRequestHandler) -> AIMessage:
+    def wrap_model_call(self, request: ModelRequest, handler: Callable[[ModelRequest], ModelResponse]) -> ModelResponse:
         if len(request.state.messages) > self.messages_threshold:
             model = advanced_model
         else:
             model = basic_model
-
-        return handler(request.replace(model=model))
+        request.model = model
+        return handler(request)
 
     def __init__(self, messages_threshold: int) -> None:
         self.messages_threshold = messages_threshold

From 59a4ae6ab56a3f94f73b66273baecd8538a1ca21 Mon Sep 17 00:00:00 2001
From: Mason Daugherty <github@mdrxy.com>
Date: Mon, 27 Oct 2025 17:01:39 -0400
Subject: [PATCH 2/2] fix

---
 src/oss/python/migrate/langchain-v1.mdx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/oss/python/migrate/langchain-v1.mdx b/src/oss/python/migrate/langchain-v1.mdx
index ec3c70933..5f8e5cfc4 100644
--- a/src/oss/python/migrate/langchain-v1.mdx
+++ b/src/oss/python/migrate/langchain-v1.mdx
@@ -368,7 +368,7 @@ class CustomState(AgentState):
 
 @tool  # [!code highlight]
 def greet(
-    runtime: ToolRuntime[CustomState]
+    runtime: ToolRuntime[None, CustomState]
 ) -> str:
     """Use this to greet the user by name."""
     user_name = runtime.state.get("user_name", "Unknown")  # [!code highlight]