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docs: Replace ModelRequestHandler with Callable[[ModelRequest], ModelResponse] #1136

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docs: Replace ModelRequestHandler with Callable[[ModelRequest], ModelResponse] #1136

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ef36046
Replace ModelRequestHandler with Callable[[ModelRequest], ModelResponse]
mcavdar Oct 27, 2025
59a4ae6
fix
mdrxy Oct 27, 2025
c54a1c2
Merge branch 'main' into patch-8
mdrxy Oct 27, 2025
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14 changes: 7 additions & 7 deletions src/oss/python/migrate/langchain-v1.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -364,7 +364,7 @@ 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]
Expand Down Expand Up @@ -488,24 +488,24 @@ 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
Expand Down