refactor(router): evict selectors only at model-list lifecycle sites, surface the rejected arg in warnings, always write strategy fields from the edit form

litellm/router.py

@@ -1194,11 +1194,11 @@ class Router:
             )
         return valid[0] if valid else None
 
-    def _build_model_group_selector(self, strategy: str, args: Mapping[str, object]) -> object | None:
+    def _build_model_group_selector(self, strategy: str, args: Mapping[str, object]) -> object | TypeError | ValueError:
         try:
             return self._build_strategy_selector(strategy=strategy, routing_strategy_args=args)
-        except (TypeError, ValueError):
-            return None
+        except (TypeError, ValueError) as exc:
+            return exc
 
     def _live_model_group_selector_keys(self) -> frozenset[str]:
         """
@@ -1246,15 +1246,14 @@ class Router:
         if cached is not None:
             verbose_router_logger.debug("routing_group=model-info model=%s strategy=%s", model, strategy)
             return strategy, cached
-        self._evict_stale_model_group_selectors()
         built: Final = self._build_model_group_selector(strategy, args)
-        if built is None:
+        if built is None or isinstance(built, Exception):
             _warn_model_group_strategy_once(
                 model,
                 "args",
                 selector_key,
                 f"model_info.routing_strategy_args for model_group '{model}' cannot initialize strategy "
-                f"'{strategy}'; falling back to the routing-group / top-level strategy.",
+                f"'{strategy}' ({built}); falling back to the routing-group / top-level strategy.",
             )
             return None
         with self._override_selectors_lock:

tests/test_litellm/proxy/management_endpoints/test_model_management_endpoints.py

@@ -771,6 +771,41 @@ class TestDeleteModelClearsRouterRegistry:
         assert mock_router.complexity_routers.get("shared-name") is config_router
 
 
+class TestUpdateDbModelMergesModelInfo:
+    def test_patch_omitting_routing_strategy_preserves_stored_value(self):
+        """
+        The UI's edit form and any partial PATCH rely on update_db_model merging
+        model_info non-destructively: keys absent from the patch keep their
+        stored value instead of being wiped.
+        """
+        import json as json_lib
+
+        from litellm.proxy.management_endpoints.model_management_endpoints import (
+            update_db_model,
+        )
+        from litellm.types.router import Deployment, ModelInfo, updateDeployment
+
+        db_model = Deployment(
+            model_name="quality",
+            litellm_params={"model": "openai/gpt-4o-mini"},
+            model_info={
+                "id": "mid-1",
+                "routing_strategy": "cost-based-routing",
+                "routing_strategy_args": {"ttl": 60},
+            },
+        )
+
+        result = update_db_model(
+            db_model=db_model,
+            updated_patch=updateDeployment(model_info=ModelInfo(id="mid-1", mode="chat")),
+        )
+
+        stored = json_lib.loads(result["model_info"])
+        assert stored["routing_strategy"] == "cost-based-routing"
+        assert stored["routing_strategy_args"] == {"ttl": 60}
+        assert stored["mode"] == "chat"
+
+
 class TestUpdateModel:
     """
     Tests for the update_model (POST /model/update) handler.

tests/test_litellm/router_strategy/test_model_group_routing_strategy.py

@@ -19,6 +19,7 @@ from litellm import Router
 from litellm.router import _warn_model_group_strategy_once
 from litellm.router_strategy.lowest_cost import LowestCostLoggingHandler
 from litellm.router_strategy.lowest_latency import LowestLatencyLoggingHandler
+from litellm.types.router import Deployment
 
 
 @pytest.fixture(autouse=True)
@@ -184,7 +185,17 @@ def test_conflict_winner_is_stable_across_model_list_order():
     assert reversed_router._get_routing_context("quality")[0] == "cost-based-routing"
 
 
-def test_invalid_args_evict_previously_cached_selector():
+def _upsert(router, model_name, model, deployment_id, model_info):
+    router.upsert_deployment(
+        Deployment(
+            model_name=model_name,
+            litellm_params={"model": model, "api_key": "sk-test", "api_base": "https://example.invalid"},
+            model_info={"id": deployment_id, **model_info},
+        )
+    )
+
+
+def test_invalid_args_evict_previously_cached_selector(caplog):
     router = _build_router(
         [
             _deployment(
@@ -198,13 +209,20 @@ def test_invalid_args_evict_previously_cached_selector():
     _, old_selector = router._get_routing_context("quality")
     assert any("|" in k for k in router._override_selectors)
 
-    for idx in router.model_name_to_deployment_indices["quality"]:
-        router.model_list[idx]["model_info"]["routing_strategy_args"] = {"ttl": "bogus"}
+    _upsert(
+        router,
+        "quality",
+        "openai/gpt-4o",
+        "d1",
+        {"routing_strategy": "latency-based-routing", "routing_strategy_args": {"ttl": "bogus"}},
+    )
 
-    strategy, _ = router._get_routing_context("quality")
+    with caplog.at_level(logging.WARNING, logger="LiteLLM Router"):
+        strategy, _ = router._get_routing_context("quality")
     assert strategy == "simple-shuffle"
     assert not any("|" in k for k in router._override_selectors)
     assert all(c is not old_selector for c in litellm.callbacks)
+    assert any("ttl" in r.getMessage() for r in caplog.records if "cannot initialize strategy" in r.getMessage())
 
 
 def test_deleting_deployment_evicts_its_selector():
@@ -309,8 +327,13 @@ def test_stale_selector_evicted_when_args_change():
     old_keys = {k for k in router._override_selectors if "|" in k}
     assert len(old_keys) == 2
 
-    for idx in router.model_name_to_deployment_indices["quality"]:
-        router.model_list[idx]["model_info"]["routing_strategy_args"] = {"ttl": 240}
+    _upsert(
+        router,
+        "quality",
+        "openai/gpt-4o",
+        "d1",
+        {"routing_strategy": "latency-based-routing", "routing_strategy_args": {"ttl": 240}},
+    )
 
     _, new_selector = router._get_routing_context("quality")
     assert new_selector is not old_selector

ui/litellm-dashboard/src/components/model_info_view.tsx

@@ -433,25 +433,13 @@ export default function ModelInfoView({
             health_check_model: values.health_check_model,
           };
         }
-        const formRoutingStrategy = values.routing_strategy ?? "";
-        if (formRoutingStrategy !== (localModelData.model_info?.routing_strategy ?? "")) {
+        if (values.routing_strategy !== undefined || values.routing_strategy_args !== undefined) {
           updatedModelInfo = {
             ...updatedModelInfo,
-            routing_strategy: formRoutingStrategy,
+            routing_strategy: values.routing_strategy ?? "",
+            routing_strategy_args: values.routing_strategy_args ? JSON.parse(values.routing_strategy_args) : {},
           };
         }
-        if (values.routing_strategy_args !== undefined) {
-          const parsedArgs = values.routing_strategy_args ? JSON.parse(values.routing_strategy_args) : {};
-          if (
-            hasRoutingStrategyArgs(parsedArgs) ||
-            hasRoutingStrategyArgs(localModelData.model_info?.routing_strategy_args)
-          ) {
-            updatedModelInfo = {
-              ...updatedModelInfo,
-              routing_strategy_args: parsedArgs,
-            };
-          }
-        }
       } catch (e) {
         NotificationsManager.fromBackend("Invalid JSON in Model Info");
         return;