fix(router): keep weighted routing when a deployment id equals a model_name

litellm/router.py

@@ -12502,7 +12502,7 @@ def _common_checks_available_deployment(
         # check if aliases set on litellm model alias map
         if specific_deployment is True:
             return model, self._get_deployment_by_litellm_model(model=model)
-        elif self.has_model_id(model):
+        elif model not in self.model_names and self.has_model_id(model):
             deployment: Final = self.get_deployment(model_id=model)
             if deployment is not None:
                 deployment_model: Final = deployment.litellm_params.model

tests/test_litellm/test_router.py

@@ -15806,3 +15806,29 @@ async def test_an_open_circuit_breaker_skips_the_session_binding_without_a_warni
     assert binding is None
     assert [record.getMessage() for record in caplog.records if record.levelno >= logging.WARNING] == []
     assert any("circuit breaker is open" in record.getMessage() for record in caplog.records)
+
+
+@pytest.mark.asyncio
+async def test_model_name_colliding_with_a_deployment_id_still_load_balances_the_group():
+    router = litellm.Router(
+        model_list=[
+            {
+                "model_name": "gpt-5-nano",
+                "litellm_params": {"model": "openai/gpt-5-nano", "api_key": "k", "weight": 0, "mock_response": "A"},
+                "model_info": {"id": "gpt-5-nano"},
+            },
+            {
+                "model_name": "gpt-5-nano",
+                "litellm_params": {"model": "openai/gpt-5-mini", "api_key": "k", "weight": 1, "mock_response": "B"},
+                "model_info": {"id": "gpt-5-mini-dep"},
+            },
+        ],
+        routing_strategy="simple-shuffle",
+    )
+
+    by_group = await router.acompletion(model="gpt-5-nano", messages=[{"role": "user", "content": "hi"}])
+    by_id = await router.acompletion(model="gpt-5-mini-dep", messages=[{"role": "user", "content": "hi"}])
+
+    assert by_group._hidden_params["model_id"] == "gpt-5-mini-dep"
+    assert by_group.choices[0].message.content == "B"
+    assert by_id._hidden_params["model_id"] == "gpt-5-mini-dep"