diff --git a/src/tagflow/tagflow.py b/src/tagflow/tagflow.py
index 5386e63..f3765d4 100644
--- a/src/tagflow/tagflow.py
+++ b/src/tagflow/tagflow.py
@@ -36,7 +36,7 @@
     WebSocket,
     WebSocketDisconnect,
 )
-from pydantic import BaseModel
+from pydantic import BaseModel, ConfigDict
 from fastapi.responses import HTMLResponse
 from fastapi.staticfiles import StaticFiles
 from starlette.middleware.base import (
@@ -602,8 +602,7 @@ class Session(BaseModel):
     send_channel: MemoryObjectSendStream[Transaction]
     transaction_receiver: MemoryObjectReceiveStream[Transaction]
 
-    class Config:
-        arbitrary_types_allowed = True
+    model_config = ConfigDict(arbitrary_types_allowed=True)
 
     @asynccontextmanager
     async def transition(self):