fix(proxy): skip auto-router baseline init when no baseline stamp exists

Pre-call hook validated metadata for every anthropic_messages request,
but _autorouter_baseline_route is only stamped for auto-routed requests.
Non-auto-routed requests raised in model_validate on every call and the
broad except turned it into a per-request noise warning, burying genuine
initialization failures. Return early when the stamp is absent; malformed
stamps still warn.

Fixes BerriAI/litellm#43658

litellm/proxy/hooks/autorouter_baseline_cache.py

@@ -133,6 +133,8 @@ class AutoRouterBaselineCache(CustomLogger):
             if logging_obj.baseline_cache_context is not None:
                 await invalidate_baseline_cache(logging_obj, "retried_request")
                 return
+            if "_autorouter_baseline_route" not in metadata:
+                return
             request: Final = _Metadata.model_validate(metadata)
             session: Final = kwargs.get("litellm_session_id") or request.session_id or logging_obj.litellm_session_id
             if not isinstance(session, str) or not session or len(session) > 256:

tests/test_litellm/proxy/hooks/test_autorouter_baseline_cache.py

@@ -1,5 +1,6 @@
 import asyncio
 import json
+import logging
 from collections.abc import AsyncIterator, Callable, Generator, Mapping
 from contextlib import contextmanager
 from datetime import datetime
@@ -324,3 +325,41 @@ async def test_provider_counting_does_not_hold_the_inference_response(
             assert _observation(await rig.capture.payload()).observation.plan is not None
     finally:
         release.set()
+
+
+async def test_missing_baseline_stamp_stays_silent_and_forged_stamp_still_warns(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture,
+) -> None:
+    rig: Final = _Rig(monkeypatch)
+    hook: Final = AutoRouterBaselineCache(None, router=lambda: None)
+    caplog.set_level(logging.WARNING, logger="LiteLLM Proxy")
+
+    async def invoke(metadata: Mapping[str, object]) -> Logging:
+        logging_obj: Final = rig.logging()
+        await hook.async_pre_call_deployment_hook(
+            {
+                "litellm_logging_obj": logging_obj,
+                "litellm_session_id": "baseline-session",
+                "litellm_metadata": metadata,
+            },
+            CallTypes.anthropic_messages,
+        )
+        return logging_obj
+
+    plain: Final = await invoke({"user_api_key_hash": "test-caller-hash"})
+    assert plain.baseline_cache_context is None
+    assert not [
+        record
+        for record in caplog.records
+        if record.getMessage() == "Auto-router baseline observation could not be initialized"
+    ]
+
+    forged: Final = await invoke(
+        {"user_api_key_hash": "test-caller-hash", "_autorouter_baseline_route": {"forged": True}}
+    )
+    assert forged.baseline_cache_context is None
+    assert [
+        record
+        for record in caplog.records
+        if record.getMessage() == "Auto-router baseline observation could not be initialized"
+    ]