diff --git a/lang_agent/base.py b/lang_agent/base.py
index ba7c2d6..19b7897 100644
--- a/lang_agent/base.py
+++ b/lang_agent/base.py
@@ -1,4 +1,4 @@
-from typing import List, Callable, TYPE_CHECKING
+from typing import List, Callable, Tuple
 from abc import ABC, abstractmethod
 from PIL import Image
 from io import BytesIO
@@ -47,4 +47,11 @@ class ToolNodeBase(GraphBase):
         """
         returns names of llm model to listen to when streaming
         """
-        return [["tool_llm"]]
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+        return [["tool_llm"]]
+    
+    def get_delay_keys(self)->Tuple[str, str]:
+        """
+        returns 2 words, one for starting delayed yeilding, the other for ending delayed yielding,
+        they should be of format ('[key1]', '[key2]')
+        """
+        return None, None
\ No newline at end of file