diff --git a/autogen/retrieve_utils.py b/autogen/retrieve_utils.py
index cd8ccbde2ed7..73d48d1587d3 100644
--- a/autogen/retrieve_utils.py
+++ b/autogen/retrieve_utils.py
@@ -34,42 +34,43 @@
 def num_tokens_from_text(
     text: str, model: str = "gpt-3.5-turbo-0613", return_tokens_per_name_and_message: bool = False
 ) -> Union[int, Tuple[int, int, int]]:
-    """Return the number of tokens used by a text."""
-    # https://github.com/openai/openai-cookbook/blob/main/examples/How_to_count_tokens_with_tiktoken.ipynb
-    try:
-        encoding = tiktoken.encoding_for_model(model)
-    except KeyError:
-        logger.debug("Warning: model not found. Using cl100k_base encoding.")
-        encoding = tiktoken.get_encoding("cl100k_base")
-    if model in {
-        "gpt-3.5-turbo-0613",
-        "gpt-3.5-turbo-16k-0613",
-        "gpt-4-0314",
-        "gpt-4-32k-0314",
-        "gpt-4-0613",
-        "gpt-4-32k-0613",
-    }:
-        tokens_per_message = 3
-        tokens_per_name = 1
-    elif model == "gpt-3.5-turbo-0301":
-        tokens_per_message = 4  # every message follows <|start|>{role/name}\n{content}<|end|>\n
-        tokens_per_name = -1  # if there's a name, the role is omitted
-    elif "gpt-3.5-turbo" in model or "gpt-35-turbo" in model:
-        logger.warning("Warning: gpt-3.5-turbo may update over time. Returning num tokens assuming gpt-3.5-turbo-0613.")
-        return num_tokens_from_text(text, model="gpt-3.5-turbo-0613")
-    elif "gpt-4" in model:
-        logger.warning("Warning: gpt-4 may update over time. Returning num tokens assuming gpt-4-0613.")
-        return num_tokens_from_text(text, model="gpt-4-0613")
+    """Return the number of tokens used by a text for different models."""
+    
+    # Define token counts for known models
+    known_models = {
+        "gpt-3.5-turbo-0613": (3, 1),
+        "gpt-3.5-turbo-16k-0613": (3, 1),
+        "gpt-4-0314": (3, 1),
+        "gpt-4-32k-0314": (3, 1),
+        "gpt-4-0613": (3, 1),
+        "gpt-4-32k-0613": (3, 1),
+    }
+    
+    # Check if the model is known and retrieve token counts
+    if model in known_models:
+        tokens_per_message, tokens_per_name = known_models[model]
     else:
-        raise NotImplementedError(
-            f"""num_tokens_from_text() is not implemented for model {model}. See """
-            f"""https://github.com/openai/openai-python/blob/main/chatml.md for information on how messages are """
-            f"""converted to tokens."""
-        )
+        logger.warning(f"Warning: Model '{model}' is not in known models. Using default token counts.")
+        # You can add support for additional models and their token counts here.
+        if model == "your-new-model-name":
+            tokens_per_message = 3
+            tokens_per_name = 1
+        else:
+            raise NotImplementedError(
+                f"num_tokens_from_text() is not implemented for model {model}. See "
+                f"https://github.com/openai/openai-python/blob/main/chatml.md for information on how messages are "
+                f"converted to tokens."
+            )
+    
+    # Use tiktoken to calculate the number of tokens in the text
+    encoding = tiktoken.encoding_for_model(model)
+    token_count = len(encoding.encode(text))
+    
     if return_tokens_per_name_and_message:
-        return len(encoding.encode(text)), tokens_per_message, tokens_per_name
+        return token_count, tokens_per_message, tokens_per_name
     else:
-        return len(encoding.encode(text))
+        return token_count
+
 
 
 def num_tokens_from_messages(messages: dict, model: str = "gpt-3.5-turbo-0613"):
diff --git a/test/test_num_tokens_from_text.py b/test/test_num_tokens_from_text.py
new file mode 100644
index 000000000000..8ce1c3f86ca6
--- /dev/null
+++ b/test/test_num_tokens_from_text.py
@@ -0,0 +1,21 @@
+import unittest
+from autogen.retrieve_utils import num_tokens_from_text
+
+class TestNumTokensFromText(unittest.TestCase):
+
+    def test_known_model(self):
+        # Test with a known model and known token counts
+        text = "This is a test message."
+        model = "gpt-3.5-turbo-0613"
+        result = num_tokens_from_text(text, model)
+        self.assertEqual(result, 6)  # Adjust the expected token count
+
+    def test_unknown_model(self):
+        # Test with an unknown model
+        text = "This is a test message."
+        model = "unknown-model"
+        with self.assertRaises(NotImplementedError):
+            num_tokens_from_text(text, model)
+
+if __name__ == '__main__':
+    unittest.main()