From 7424673d00361f063021e204015ba48b8aefdf01 Mon Sep 17 00:00:00 2001
From: apex-mochen <2756823972@qq.com>
Date: Sat, 3 Oct 2026 13:32:13 +0800
Subject: [PATCH] fix(complexity_router): invalidate stale pins on new user
 asks

Signed-off-by: apex-mochen <2756823972@qq.com>
---
 .../complexity_router/complexity_router.py    |  7 ++
 .../router_strategy/test_complexity_router.py | 86 +++++++++++++++++++
 2 files changed, 93 insertions(+)

diff --git a/litellm/router_strategy/complexity_router/complexity_router.py b/litellm/router_strategy/complexity_router/complexity_router.py
index 3610991a20d..3a8edf0c144 100644
--- a/litellm/router_strategy/complexity_router/complexity_router.py
+++ b/litellm/router_strategy/complexity_router/complexity_router.py
@@ -4390,6 +4390,13 @@ class ComplexityRouter(CustomLogger):
                         )
                     )
 
+        if (
+            cache_key is not None
+            and not pin_replay_allowed
+            and self._matched_plan_mode_signal(request_kwargs, resolved_messages) is None
+        ):
+            await self.litellm_router_instance.cache.async_delete_cache(key=cache_key)
+
         routed_response: Final = await self._classify_and_route(
             model=model,
             request_kwargs=request_kwargs,
diff --git a/tests/unit/router_strategy/test_complexity_router.py b/tests/unit/router_strategy/test_complexity_router.py
index 333524ffffc..f81e7cd609d 100644
--- a/tests/unit/router_strategy/test_complexity_router.py
+++ b/tests/unit/router_strategy/test_complexity_router.py
@@ -16961,3 +16961,89 @@ class TestNonReasoningTier:
             "complex",
             "reasoning",
         )
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("circuit_breaker_enabled", [True, False])
+async def test_new_user_ask_classifier_failure_clears_previous_turn_pin(circuit_breaker_enabled: bool) -> None:
+    from openai import AsyncOpenAI
+
+    outcomes: Final = iter(("SIMPLE", None, "COMPLEX"))
+
+    def classifier_response(request: httpx.Request) -> httpx.Response:
+        tier: Final = next(outcomes)
+        if tier is None:
+            raise httpx.ReadTimeout("classifier unavailable", request=request)
+        return httpx.Response(
+            200,
+            json={
+                "id": "classification",
+                "object": "chat.completion",
+                "created": 0,
+                "model": "classifier",
+                "choices": [
+                    {
+                        "index": 0,
+                        "finish_reason": "stop",
+                        "message": {"role": "assistant", "content": json.dumps({"tier": tier})},
+                    }
+                ],
+                "usage": {"prompt_tokens": 1, "completion_tokens": 1, "total_tokens": 2},
+            },
+        )
+
+    async with httpx.AsyncClient(transport=httpx.MockTransport(classifier_response)) as transport:
+        async with AsyncOpenAI(api_key="synthetic", http_client=transport, max_retries=0) as client:
+            underlying: Final = Router(
+                default_litellm_params={"client": client},
+                model_list=[
+                    {"model_name": "judge", "litellm_params": {"model": "openai/classifier", "api_key": "synthetic"}},
+                    {"model_name": "cheap", "litellm_params": {"model": "openai/cheap"}},
+                    {"model_name": "default", "litellm_params": {"model": "openai/default"}},
+                ],
+            )
+            router: Final = ComplexityRouter(
+                "auto",
+                underlying,
+                {
+                    "classifier_type": "llm",
+                    "classification_mode": "user_turn",
+                    "classifier_context_include_assistant_turns": True,
+                    "classifier_llm_config": {
+                        "model": "judge",
+                        "classification_rubric": "agentic",
+                        "circuit_breaker_enabled": circuit_breaker_enabled,
+                    },
+                    "classifier_fallback": "default_model",
+                    "default_model": "default",
+                    "tiers": {"SIMPLE": "cheap", "MEDIUM": "default", "COMPLEX": "default", "REASONING": "default"},
+                },
+            )
+            kwargs: Final = {"metadata": {"session_id": "stale-pin-regression"}}
+            first: Final = [{"role": "user", "content": "Hello"}]
+            second: Final = [
+                *first,
+                {"role": "assistant", "content": "Hello!"},
+                {"role": "user", "content": "Fix the queue worker"},
+            ]
+            continuation: Final = [
+                *second,
+                {
+                    "role": "assistant",
+                    "content": None,
+                    "tool_calls": [
+                        {"id": "t1", "type": "function", "function": {"name": "read_file", "arguments": "{}"}}
+                    ],
+                },
+                {"role": "tool", "tool_call_id": "t1", "content": "File contents"},
+            ]
+            responses: Final = [
+                await router.async_pre_routing_hook("auto", kwargs, messages=messages)
+                for messages in (first, second, continuation)
+            ]
+            assert [response.model for response in responses] == ["cheap", "default", "default"]
+            assert [response.routing_decision["cause"] for response in responses] == [
+                "llm_classifier",
+                "default_model_fallback",
+                "default_model_fallback" if circuit_breaker_enabled else "llm_classifier",
+            ]