fix(otel): keep credentialless fallback on base path

litellm/litellm_core_utils/litellm_logging.py

@@ -4803,17 +4803,11 @@ def _maybe_construct_otel_v2(callback_name: str, _in_memory_loggers: list[Custom
     ``callback_name`` — callers should then fall through to the legacy path.
 
     A preset that needs operator credentials it cannot find is allowed to build
-    anyway, exporting nowhere, only while this request has a key/team destination
-    for that backend: the exporter-less logger exists to let the fan-out carry those
-    spans without a second detached copy. With no such destination the preset raises
-    as it always did and the caller falls through to the legacy path, so the proxy
-    never publishes a provider that exports nowhere for a backend the operator
-    configured and no tenant can use.
-
-    The degraded preset keeps the operator's generic OTLP collector, so a proxy whose
-    only v2 backend is that preset still reaches it. Beside another v2 logger the
-    collector is already that logger's, and a second copy of every model span from
-    this one would land there too, so only the credential-gated exporter is kept.
+    only when this request has a key/team destination for that backend and another
+    V2 logger is already registered to carry the fan-out. The resulting logger keeps
+    only its credential-gated exporter, while the registered logger owns operator
+    delivery. Without that carrier, the preset raises as it always did and the
+    caller falls through to the legacy path.
     """
     from litellm.integrations.otel.model.config import is_otel_v2_enabled
 
@@ -4827,6 +4821,7 @@ def _maybe_construct_otel_v2(callback_name: str, _in_memory_loggers: list[Custom
     if preset_fn is None:
         return None
     serves_a_destination: Final = callback_name in destination_backends()
+    has_v2_logger: Final = any(isinstance(callback, OpenTelemetryV2) for callback in _in_memory_loggers)
     for callback in _in_memory_loggers:
         if (
             isinstance(callback, OpenTelemetryV2)
@@ -4835,16 +4830,12 @@ def _maybe_construct_otel_v2(callback_name: str, _in_memory_loggers: list[Custom
         ):
             return callback
     try:
-        built: Final = preset_fn(allow_missing_credentials=serves_a_destination)
+        built: Final = preset_fn(allow_missing_credentials=serves_a_destination and has_v2_logger)
     except Exception:
         # If env vars are missing or the preset raises, defer to the legacy path
         # so customers get the same error story they had before V2 landed.
         return None
-    config: Final = (
-        _only_the_gated_exporter(built)
-        if _is_credential_gated(built) and any(isinstance(callback, OpenTelemetryV2) for callback in _in_memory_loggers)
-        else built
-    )
+    config: Final = _only_the_gated_exporter(built) if _is_credential_gated(built) else built
     if _exports_nowhere(config):
         verbose_logger.warning(
             "OTel V2: no operator credentials for '%s'; only key/team destinations will receive its traces",

tests/test_litellm/integrations/otel/test_otel_v2_destinations.py

@@ -1123,21 +1123,22 @@ class TestPresetDegradation:
         with pytest.raises(ValueError, match="LANGFUSE_PUBLIC_KEY"):
             langfuse_preset()
 
-    def test_a_credential_less_proxy_builds_the_v2_logger_for_a_team_destination(self, monkeypatch):
+    def test_a_credential_less_proxy_builds_the_gated_logger_beside_a_v2_carrier(self, monkeypatch):
         from litellm.litellm_core_utils.litellm_logging import _maybe_construct_otel_v2
 
         credential_less_proxy(monkeypatch)
         monkeypatch.setenv("LITELLM_OTEL_V2", "true")
+        carrier = build_otel_v2_logger(OpenTelemetryV2Config(exporter="in_memory"))
 
         def run():
             set_request_destinations((LANGFUSE_DEST,))
-            return _maybe_construct_otel_v2("langfuse_otel", [])
+            return _maybe_construct_otel_v2("langfuse_otel", [carrier])
 
         is_otel_v2_enabled.cache_clear()
         logger = in_fresh_context(run)
         is_otel_v2_enabled.cache_clear()
 
-        assert logger is not None, "team-only deployments must not fall back to the legacy integration"
+        assert logger is not None
         assert all(spec.requires_headers and not spec.headers for spec in logger.config.exporters)
 
     def test_a_credential_less_proxy_with_no_destinations_falls_back_to_the_legacy_path(self, monkeypatch):
@@ -1179,7 +1180,7 @@ class TestPresetDegradation:
 
         credential_less_proxy(monkeypatch)
         monkeypatch.setenv("LITELLM_OTEL_V2", "true")
-        loggers = []
+        loggers = [build_otel_v2_logger(OpenTelemetryV2Config(exporter="in_memory"))]
 
         def with_destination():
             set_request_destinations((LANGFUSE_DEST,))
@@ -1237,10 +1238,21 @@ class TestPresetDegradation:
         assert [spec.endpoint for spec in logger.config.exporters] == [None]
         assert all(spec.requires_headers and not spec.headers for spec in logger.config.exporters)
 
-    def test_a_degraded_logger_on_its_own_keeps_the_operator_collector(self, monkeypatch):
-        logger = self._degraded_langfuse_beside([], monkeypatch)
+    def test_a_credential_less_proxy_with_a_destination_but_no_v2_carrier_falls_back(self, monkeypatch):
+        from litellm.litellm_core_utils.litellm_logging import _maybe_construct_otel_v2
 
-        assert [spec.endpoint for spec in logger.config.exporters] == ["http://collector.local:4318", None]
+        credential_less_proxy(monkeypatch)
+        monkeypatch.setenv("LITELLM_OTEL_V2", "true")
+
+        def run():
+            set_request_destinations((LANGFUSE_DEST,))
+            return _maybe_construct_otel_v2("langfuse_otel", [])
+
+        is_otel_v2_enabled.cache_clear()
+        logger = in_fresh_context(run)
+        is_otel_v2_enabled.cache_clear()
+
+        assert logger is None
 
     def test_a_credentialed_logger_beside_another_v2_logger_keeps_every_exporter(self, monkeypatch):
         """Only a degraded preset gives the collector up; an operator who configured
@@ -1249,6 +1261,7 @@ class TestPresetDegradation:
 
         monkeypatch.setenv("LANGFUSE_PUBLIC_KEY", "pk-lf-1")
         monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-1")
+        monkeypatch.setenv("LANGFUSE_HOST", "https://cloud.langfuse.com")
         monkeypatch.setenv("OTEL_EXPORTER_OTLP_ENDPOINT", "http://collector.local:4318")
         monkeypatch.setenv("LITELLM_OTEL_V2", "true")
         collector_logger = build_otel_v2_logger(OpenTelemetryV2Config(exporter="in_memory"))