diff --git a/litellm/router_strategy/complexity_router/complexity_router.py b/litellm/router_strategy/complexity_router/complexity_router.py
index c82e47d14a5..61bfeba42da 100644
--- a/litellm/router_strategy/complexity_router/complexity_router.py
+++ b/litellm/router_strategy/complexity_router/complexity_router.py
@@ -926,9 +926,17 @@ class ComplexityRouter(CustomLogger):
 
         Reads the router's in-process deployment list, so it costs no I/O: the cooldown
         set was already fetched once for the whole request.
+
+        A deployment with no id counts as live. Cooldowns are keyed by id, so one that
+        cannot be identified can never be known to be cooling, and the ladder's rule
+        everywhere else is that an absent health signal means live. Excluding it instead
+        would let missing metadata empty a tier and push traffic to a pricier one.
         """
         deployments = self.litellm_router_instance.get_model_list(model_name=model) or ()
-        return any(self._deployment_id(deployment) not in cooled_down for deployment in deployments)
+        return any(
+            deployment_id is None or deployment_id not in cooled_down
+            for deployment_id in map(self._deployment_id, deployments)
+        )
 
     @staticmethod
     def _deployment_id(deployment: Mapping[str, Any]) -> str | None:
diff --git a/tests/test_litellm/router_strategy/test_complexity_router.py b/tests/test_litellm/router_strategy/test_complexity_router.py
index 3188d68cd2d..634c562a38b 100644
--- a/tests/test_litellm/router_strategy/test_complexity_router.py
+++ b/tests/test_litellm/router_strategy/test_complexity_router.py
@@ -4933,6 +4933,28 @@ class TestTierFallbackLadder:
         assert response.model == "medium-model"
         assert response.routing_decision["tier_fallback_from"] == "SIMPLE"
 
+    @pytest.mark.asyncio
+    async def test_a_deployment_with_no_id_counts_as_live(self):
+        """Cooldowns are keyed by deployment id, so one without an id can never be known to
+        be cooling. It counts as live, matching the rule everywhere else that an absent
+        health signal means live; excluding it would let missing metadata empty a tier and
+        push traffic to a pricier one."""
+
+        class IdlessRouter(StubRouter):
+            def get_model_list(self, model_name=None, team_id=None):
+                self.listed.append(model_name)
+                return [{"model_info": {}}] if model_name in self.registered else []
+
+        router = ComplexityRouter(
+            model_name="test-ladder-router",
+            litellm_router_instance=IdlessRouter(live=set()),
+            complexity_router_config={"tiers": dict(LADDER_TIERS), "session_affinity": False},
+        )
+        response = await _route(router, "What is 2+2?")
+        assert response.model in {"simple-a", "simple-b"}
+        assert "tier_fallback_from" not in response.routing_decision
+        assert "resolved_by" not in response.routing_decision
+
     @pytest.mark.asyncio
     async def test_health_lookup_failure_keeps_the_classified_tier(self):
         """A health view that cannot be read must not empty every tier and push traffic up