diff --git a/backend/apps/chat/api/chat.py b/backend/apps/chat/api/chat.py
index 49e1b43d..028567a3 100644
--- a/backend/apps/chat/api/chat.py
+++ b/backend/apps/chat/api/chat.py
@@ -175,8 +175,13 @@ async def start_chat(session: SessionDep, current_user: CurrentUser, create_chat
 async def start_chat(session: SessionDep, current_user: CurrentUser, current_assistant: CurrentAssistant,
                      create_chat_obj: CreateChat = CreateChat(origin=2)):
     try:
-        return create_chat(session, current_user, create_chat_obj, create_chat_obj and create_chat_obj.datasource,
-                           current_assistant)
+        # create_chat 内会经 AssistantOutDsFactory.get_instance 同步请求宿主 API
+        # （requests.get，默认 10s 超时），必须放工作线程执行，避免阻塞事件循环（Issue #1288）
+        def inner():
+            return create_chat(session, current_user, create_chat_obj, create_chat_obj and create_chat_obj.datasource,
+                               current_assistant)
+
+        return await asyncio.to_thread(inner)
     except Exception as e:
         raise HTTPException(
             status_code=500,
diff --git a/backend/apps/chat/task/llm.py b/backend/apps/chat/task/llm.py
index 55a01b01..cd6fc203 100644
--- a/backend/apps/chat/task/llm.py
+++ b/backend/apps/chat/task/llm.py
@@ -1,3 +1,4 @@
+import asyncio
 import concurrent
 import json
 import os
@@ -235,7 +236,10 @@ async def create(cls, *args, **kwargs):
                 specialized_model_id = args[2].custom_model
                 print("use custom model: id[" + specialized_model_id + "]")
         config: LLMConfig = await get_default_config(specialized_model_id)
-        instance = cls(*args, **kwargs, config=config)
+        # 构造函数可能同步调用宿主 API（type==1 高级应用动态数据源，
+        # LLMService.__init__ -> AssistantOutDsFactory.get_instance -> requests.get），
+        # 必须在工作线程执行，避免阻塞事件循环（Issue #1288）
+        instance = await asyncio.to_thread(cls, *args, **kwargs, config=config)
 
         chat_params: list[SysArgModel] = await get_groups(args[0], "chat")
         for config in chat_params:
diff --git a/backend/apps/system/api/assistant.py b/backend/apps/system/api/assistant.py
index d35da977..663426b5 100644
--- a/backend/apps/system/api/assistant.py
+++ b/backend/apps/system/api/assistant.py
@@ -1,3 +1,4 @@
+import asyncio
 import json
 import os
 from datetime import datetime, timedelta, timezone
@@ -285,7 +286,12 @@ async def ds(session: SessionDep, current_assistant: CurrentAssistant):
             }
             for ds in db_ds_list]
     if current_assistant.type == 1:
-        out_ds_instance: AssistantOutDs = AssistantOutDsFactory.get_instance(current_assistant)
+        # 构造 AssistantOutDs 会同步请求宿主 API（requests.get，默认 10s 超时），
+        # 必须在工作线程执行，避免阻塞事件循环导致宿主回调死锁（Issue #1288）
+        def inner():
+            return AssistantOutDsFactory.get_instance(current_assistant)
+
+        out_ds_instance: AssistantOutDs = await asyncio.to_thread(inner)
         return [
             {
                 "id": str(ds.id),