diff --git a/fastapi_server/fake_stream_server_dashscopy.py b/fastapi_server/fake_stream_server_dashscopy.py
index 59bb656..d401462 100644
--- a/fastapi_server/fake_stream_server_dashscopy.py
+++ b/fastapi_server/fake_stream_server_dashscopy.py
@@ -33,7 +33,7 @@ class DSApplicationCallRequest(BaseModel):
     messages: List[DSMessage]
     stream: bool = Field(default=True)
     # Optional overrides for pipeline behavior
-    thread_id: Optional[int] = Field(default=3)
+    thread_id: Optional[str] = Field(default="3")
 
 
 app = FastAPI(title="DashScope-Compatible Application API",
diff --git a/fastapi_server/server_dashscope.py b/fastapi_server/server_dashscope.py
index 3b6582b..deb3bfb 100644
--- a/fastapi_server/server_dashscope.py
+++ b/fastapi_server/server_dashscope.py
@@ -33,7 +33,7 @@ class DSApplicationCallRequest(BaseModel):
     messages: List[DSMessage]
     stream: bool = Field(default=True)
     # Optional overrides for pipeline behavior
-    thread_id: Optional[int] = Field(default=3)
+    thread_id: Optional[str] = Field(default="3")
 
 
 app = FastAPI(title="DashScope-Compatible Application API",
diff --git a/fastapi_server/server_openai.py b/fastapi_server/server_openai.py
index 1fa4c0d..c5283ec 100644
--- a/fastapi_server/server_openai.py
+++ b/fastapi_server/server_openai.py
@@ -33,7 +33,7 @@ class OpenAIChatCompletionRequest(BaseModel):
     temperature: Optional[float] = Field(default=1.0)
     max_tokens: Optional[int] = Field(default=None)
     # Optional overrides for pipeline behavior
-    thread_id: Optional[int] = Field(default=3)
+    thread_id: Optional[str] = Field(default='3')
 
 
 app = FastAPI(
diff --git a/lang_agent/pipeline.py b/lang_agent/pipeline.py
index 3401e21..350e9e7 100644
--- a/lang_agent/pipeline.py
+++ b/lang_agent/pipeline.py
@@ -145,7 +145,7 @@ class Pipeline:
         async for chunk in out:
             yield chunk
 
-    def chat(self, inp:str, as_stream:bool=False, as_raw:bool=False, thread_id:int = None):
+    def chat(self, inp:str, as_stream:bool=False, as_raw:bool=False, thread_id:str = '3'):
         """
         as_stream (bool): if true, enable the thing to be streamable
         as_raw (bool): return full dialoge of List[SystemMessage, HumanMessage, ToolMessage]
@@ -153,7 +153,6 @@ class Pipeline:
         # NOTE: this prompt will be overwritten by 'configs/route_sys_prompts/chat_prompt.txt' for route graph
         u = DEFAULT_PROMPT
 
-        thread_id = thread_id if thread_id is not None else 3
         inp = {"messages":[SystemMessage(u),
                            HumanMessage(inp)]}, {"configurable": {"thread_id": thread_id}}
 
@@ -188,7 +187,7 @@ class Pipeline:
         
         assert 0, "something is wrong"
 
-    async def achat(self, inp:str, as_stream:bool=False, as_raw:bool=False, thread_id:int = None):
+    async def achat(self, inp:str, as_stream:bool=False, as_raw:bool=False, thread_id:str = '3'):
         """
         Async version of chat using LangGraph's native async support.
         
@@ -198,7 +197,6 @@ class Pipeline:
         # NOTE: this prompt will be overwritten by 'configs/route_sys_prompts/chat_prompt.txt' for route graph
         u = DEFAULT_PROMPT
 
-        thread_id = thread_id if thread_id is not None else 3
         inp_data = {"messages":[SystemMessage(u),
                            HumanMessage(inp)]}, {"configurable": {"thread_id": thread_id}}