diff --git a/litellm/integrations/langfuse/langfuse_otel.py b/litellm/integrations/langfuse/langfuse_otel.py
index e564766eabb..70734b8ba96 100644
--- a/litellm/integrations/langfuse/langfuse_otel.py
+++ b/litellm/integrations/langfuse/langfuse_otel.py
@@ -154,9 +154,7 @@ class LangfuseOtelLogger(OpenTelemetry):
         return _extract_output_items(response_obj) or _extract_choices_output(response_obj)
 
     @staticmethod
-    def _trace_tags(
-        kwargs: Mapping[str, object], metadata: Mapping[str, object], derive_defaults: bool = True
-    ) -> tuple[str, ...]:
+    def _trace_tags(kwargs: Mapping[str, object], metadata: Mapping[str, object]) -> tuple[str, ...]:
         """Order-preserving dedupe of caller tags, request tags and langfuse_default_tags expansions."""
         import litellm
 
@@ -184,16 +182,15 @@ class LangfuseOtelLogger(OpenTelemetry):
 
         expanded: Final = tuple(_default_tag(key) for key in default_tags) if isinstance(default_tags, list) else ()
         candidates: Final = (
-            (caller_tags,)
-            if isinstance(caller_tags, str)
-            else tuple(tag for tag in caller_tags if isinstance(tag, str))
-            if isinstance(caller_tags, list)
-            else ()
-        ) + (
-            (tuple(tag for tag in request_tags if isinstance(tag, str)) if isinstance(request_tags, list) else ())
+            (
+                (caller_tags,)
+                if isinstance(caller_tags, str)
+                else tuple(tag for tag in caller_tags if isinstance(tag, str))
+                if isinstance(caller_tags, list)
+                else ()
+            )
+            + (tuple(tag for tag in request_tags if isinstance(tag, str)) if isinstance(request_tags, list) else ())
             + tuple(tag for tag in expanded if tag is not None)
-            if derive_defaults
-            else ()
         )
         return tuple(dict.fromkeys(candidates))
 
@@ -232,9 +229,10 @@ class LangfuseOtelLogger(OpenTelemetry):
                 f"litellm-{kwargs.get('call_type') or 'completion'}",
             )
 
-        tags: Final = LangfuseOtelLogger._trace_tags(kwargs, metadata, derive_defaults=not joins_existing_trace)
-        if tags:
-            safe_set_attribute(span, LangfuseSpanAttributes.TAGS.value, json.dumps(list(tags)))
+        if not joins_existing_trace:
+            tags: Final = LangfuseOtelLogger._trace_tags(kwargs, metadata)
+            if tags:
+                safe_set_attribute(span, LangfuseSpanAttributes.TAGS.value, json.dumps(list(tags)))
 
         input_json: Final = safe_dumps(kwargs.get("messages")) if kwargs.get("messages") else None
         if input_json is not None:
diff --git a/tests/test_litellm/integrations/test_langfuse_otel.py b/tests/test_litellm/integrations/test_langfuse_otel.py
index 57600e2ebd2..b4f5e6d96dd 100644
--- a/tests/test_litellm/integrations/test_langfuse_otel.py
+++ b/tests/test_litellm/integrations/test_langfuse_otel.py
@@ -219,7 +219,6 @@ class TestLangfuseOtelIntegration:
                 LangfuseSpanAttributes.TRACE_USER_ID.value: "user-123",
                 LangfuseSpanAttributes.SESSION_ID.value: "sess-456",
                 # Lists / dicts should be JSON strings
-                LangfuseSpanAttributes.TAGS.value: json.dumps(["tagA", "tagB"]),
                 LangfuseSpanAttributes.TRACE_NAME.value: "trace-name",
                 LangfuseSpanAttributes.TRACE_ID.value: "traceid",  # stripped dashes
                 LangfuseSpanAttributes.TRACE_METADATA.value: json.dumps({"k": "v"}),
@@ -1033,7 +1032,7 @@ class TestDerivedTraceFields:
                 "messages": [{"role": "user", "content": "hi"}],
                 "cache_hit": True,
                 "litellm_params": {
-                    "metadata": {"existing_trace_id": "abc123", "tags": ["mine"]},
+                    "metadata": {"existing_trace_id": "abc123", "tags": ["experiment"]},
                 },
                 "standard_logging_object": {"request_tags": ["injected"]},
             },
@@ -1043,9 +1042,9 @@ class TestDerivedTraceFields:
         assert attributes["langfuse.trace.existing_id"] == "abc123"
         assert "langfuse.trace.input" not in attributes
         assert "langfuse.trace.output" not in attributes
+        assert "langfuse.trace.tags" not in attributes
         assert "langfuse.observation.input" in attributes
         assert "langfuse.observation.output" in attributes
-        assert json.loads(attributes["langfuse.trace.tags"]) == ["mine"]
 
     def test_responses_api_output_mirrors_observation_output_items(self):
         from openai.types.responses import ResponseFunctionToolCall