fix(otel): skip only token-array entries so chat Message objects keep their output messages

litellm/integrations/opentelemetry.py

@@ -2823,7 +2823,7 @@ class OpenTelemetry(OTELGenAISemconvMixin, CustomLogger):
         primitive_value: Final = self._cast_as_primitive_value_type(value)
         span.set_attribute(key, primitive_value)
 
-    def _transform_messages_to_otel_semantic_conventions(self, messages: list[dict] | str) -> list[dict]:
+    def _transform_messages_to_otel_semantic_conventions(self, messages: list[Any] | str) -> list[dict]:
         """
         Transforms LiteLLM/OpenAI style messages into OTEL GenAI 1.38 compliant format.
         OTEL expects a 'parts' array instead of a single 'content' string.
@@ -2841,7 +2841,8 @@ class OpenTelemetry(OTELGenAISemconvMixin, CustomLogger):
         for msg in messages:
             # An embedding's input is logged as its messages, so a token-array input
             # (`[[9906, 1917]]` or `[9906, 1917]`) yields lists or ints with no role or content.
-            if not isinstance(msg, dict):
+            # Anything else is message-like: a dict, or a `Message` object from chat output.
+            if isinstance(msg, (list, int)):
                 continue
             role = msg.get("role", "user")
             content = msg.get("content", "")

tests/unit/integrations/test_opentelemetry.py

@@ -3344,6 +3344,19 @@ class TestOpenTelemetrySemanticConventions138(unittest.TestCase):
         self.assertEqual(json.loads(attrs["gen_ai.input.messages"]), [])
         self.assertEqual(attrs["gen_ai.operation.name"], "aembedding")
 
+    def test_choice_message_objects_are_still_transformed(self):
+        """
+        Chat output reaches the message conversion as `Message` objects, not dicts, so
+        skipping token-array entries must not skip them.
+        """
+        from litellm.types.utils import Choices, Message
+
+        choices = [Choices(finish_reason="stop", index=0, message=Message(role="assistant", content="Hi"))]
+        self.assertEqual(
+            OpenTelemetry()._transform_choices_to_otel_semantic_conventions(choices),
+            [{"role": "assistant", "parts": [{"type": "text", "content": "Hi"}], "finish_reason": "stop"}],
+        )
+
     def test_output_messages_uses_parts_structure(self):
         """
         Test that gen_ai.output.messages uses the OTEL 1.38 parts array structure.