fix(router): validate routing_groups at save time and keep invalid DB groups from blocking SSO load

Overlapping routing_groups persisted from the Admin UI raised inside
Router._init_routing_groups during the DB config reconcile, which skipped
loading SSO, guardrails and the other DB-backed settings while leaving the
proxy healthy. /config/update now returns 400 for overlapping models,
duplicate names, the reserved default name and unknown strategies before
writing, the Router builds every group selector before replacing its state
so a rejected update keeps the previous groups routing, and the proxy applies
routing_groups separately from the other router settings so an already
persisted invalid value is logged and skipped instead of aborting the
reconcile. The Admin UI modal blocks picking a model another group owns.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/proxy/proxy_server.py

@@ -143,6 +143,7 @@ from litellm.router_utils.auto_router_tuning_baseline import (
     snapshot_tuning_baselines,
     tuning_limit_violation,
 )
+from litellm.router_utils.routing_groups import parse_routing_groups
 from litellm.types.caching import RedisPipelineIncrementOperation
 from litellm.types.utils import (
     ModelResponse,
@@ -759,6 +760,7 @@ from litellm.types.router import (
     ClassifierPlugin,
     DeploymentTypedDict,
     RouterGeneralSettings,
+    RoutingGroup,
     RoutingPlugin,
     SearchToolTypedDict,
     updateDeployment,
@@ -6896,7 +6898,27 @@ class ProxyConfig:
                 combined_router_settings = db_router_settings.param_value
 
             if combined_router_settings:
-                llm_router.update_settings(**combined_router_settings)
+                self._apply_router_settings(llm_router, combined_router_settings)
+
+    @staticmethod
+    def _apply_router_settings(llm_router: Router, router_settings: Mapping[str, object]) -> None:
+        """
+        `routing_groups` is applied on its own so a value persisted before
+        save-time validation existed cannot abort the reconcile that also loads
+        SSO, guardrails and the other DB-backed settings. The router keeps the
+        groups it already holds when the new value is rejected.
+        """
+        llm_router.update_settings(**{k: v for k, v in router_settings.items() if k != "routing_groups"})
+        if "routing_groups" not in router_settings:
+            return
+        try:
+            llm_router.update_settings(routing_groups=router_settings["routing_groups"])
+        except (TypeError, ValueError) as invalid_groups:
+            verbose_proxy_logger.error(
+                "Ignoring invalid router_settings.routing_groups from config/DB, all other router settings still "
+                "apply. Fix the routing groups in the Admin UI to load them: %s",
+                invalid_groups,
+            )
 
     def _add_general_settings_from_db_config(
         self, config_data: dict, general_settings: dict, proxy_logging_obj: ProxyLogging
@@ -16903,6 +16925,12 @@ async def update_config(
                         )
                     },
                 )
+            try:
+                parse_routing_groups(
+                    TypeAdapter(list[RoutingGroup] | None).validate_python(raw_router_settings.get("routing_groups"))
+                )
+            except (ValidationError, ValueError) as invalid_groups:
+                raise HTTPException(status_code=400, detail={"error": str(invalid_groups)})
 
         if prisma_client is None:
             raise Exception("No DB Connected")

litellm/router.py

@@ -218,6 +218,7 @@ from litellm.router_utils.router_callbacks.track_deployment_metrics import (
     increment_deployment_failures_for_current_minute,
     increment_deployment_successes_for_current_minute,
 )
+from litellm.router_utils.routing_groups import parse_routing_groups, validate_routing_strategy
 from litellm.scheduler import FlowItem, Scheduler
 from litellm.types.llms.openai import (
     AllMessageValues,
@@ -1244,20 +1245,9 @@ class Router:
             return strategy.value
         return strategy
 
-    def _validate_routing_strategy(self, routing_strategy: RoutingStrategy | str | None) -> None:
-        # See: https://github.com/BerriAI/litellm/issues/11330
-        valid_strategy_strings: Final = ["simple-shuffle", "lar1"] + [s.value for s in RoutingStrategy]
-        if routing_strategy is None:
-            return
-        is_valid_string: Final = isinstance(routing_strategy, str) and routing_strategy in valid_strategy_strings
-        is_valid_enum: Final = isinstance(routing_strategy, RoutingStrategy)
-        if not is_valid_string and not is_valid_enum:
-            raise ValueError(
-                f"Invalid routing_strategy: '{routing_strategy}'. "
-                f"Valid options: {valid_strategy_strings}. "
-                f"Check 'router_settings.routing_strategy' in your config.yaml "
-                f"or the 'routing_strategy' parameter if using the Router SDK directly."
-            )
+    @staticmethod
+    def _validate_routing_strategy(routing_strategy: RoutingStrategy | str | None) -> None:
+        validate_routing_strategy(routing_strategy)
 
     def _build_strategy_selector(
         self,
@@ -1274,11 +1264,6 @@ class Router:
         match self._normalize_strategy(strategy):
             case RoutingStrategy.LEAST_BUSY.value:
                 selector = LeastBusyLoggingHandler(router_cache=self.cache)
-                if register_callbacks:
-                    if isinstance(litellm.input_callback, list):
-                        litellm.logging_callback_manager.add_litellm_input_callback(selector)
-                    else:
-                        litellm.input_callback = [selector]
             case RoutingStrategy.USAGE_BASED_ROUTING.value:
                 selector = LowestTPMLoggingHandler(
                     router_cache=self.cache,
@@ -1302,11 +1287,21 @@ class Router:
             case _:
                 pass
 
-        if selector is not None and register_callbacks and isinstance(litellm.callbacks, list):
-            litellm.logging_callback_manager.add_litellm_callback(selector)
+        if selector is not None and register_callbacks:
+            self._register_router_selector(selector)
 
         return selector
 
+    @staticmethod
+    def _register_router_selector(selector: RouterStrategySelector) -> None:
+        if isinstance(selector, LeastBusyLoggingHandler):
+            if isinstance(litellm.input_callback, list):
+                litellm.logging_callback_manager.add_litellm_input_callback(selector)
+            else:
+                litellm.input_callback = [selector]
+        if isinstance(litellm.callbacks, list):
+            litellm.logging_callback_manager.add_litellm_callback(selector)
+
     def _unregister_router_selectors(self, selectors: Sequence[object]) -> None:
         """
         Drop router-owned strategy selectors from litellm's global callback
@@ -1397,75 +1392,69 @@ class Router:
         at most one explicit group. Constructs per-group strategy selectors so
         groups with different `routing_strategy_args` track independent state.
 
+        Validation and selector construction run to completion before any
+        router state changes, so a rejected input raises with the previously
+        loaded groups still routing.
+
         Models not claimed by any explicit group are served by the implicit
         `"default"` group, whose selectors are the `self.<strategy>_logger`
         attributes set up in `routing_strategy_init`.
         """
-        group_selectors: Final[Mapping[str, Mapping[str, RouterStrategySelector]]] = getattr(
-            self, "_group_selectors", {}
-        )
-        self._unregister_router_selectors([sel for selectors in group_selectors.values() for sel in selectors.values()])
-
-        self._routing_groups: dict[str, RoutingGroup] = {}
-        self._model_to_group: dict[str, str] = {}
-        self._group_selectors: dict[str, dict[str, RouterStrategySelector]] = {}
-        self._invalidate_model_group_info_cache()
-        self._invalidate_access_groups_cache()
-
         if not groups_input:
+            self._replace_routing_groups(())
             return
 
-        known_model_names: Final = {m.get("model_name") for m in (self.model_list or []) if m.get("model_name")}
+        known_model_names: Final = frozenset(m["model_name"] for m in (self.model_list or ()) if m.get("model_name"))
+        groups: Final = parse_routing_groups(groups_input, known_model_names=known_model_names)
 
-        seen_group_names: Final[set] = set()
-        for raw in groups_input:
-            group = raw if isinstance(raw, RoutingGroup) else RoutingGroup(**raw)
-
-            if not group.group_name:
-                raise ValueError("routing_groups: group_name must be non-empty.")
-            if group.group_name == "default":
-                raise ValueError("routing_groups: 'default' is reserved for the implicit fallback group.")
-            if group.group_name in known_model_names or group.group_name in (self.model_group_alias or {}):
+        alias_names: Final = frozenset(self.model_group_alias or ())
+        for group in groups:
+            if group.group_name in known_model_names or group.group_name in alias_names:
                 verbose_router_logger.warning(
                     "routing_groups: group_name '%s' is shadowed by an existing model_name or model_group_alias; "
                     "the group's strategy still applies to its members, but the name is not callable until renamed.",
                     group.group_name,
                 )
-            if group.group_name in seen_group_names:
-                raise ValueError(
-                    f"routing_groups: group names must be unique, duplicate group_name '{group.group_name}'."
-                )
-            seen_group_names.add(group.group_name)
 
-            self._validate_routing_strategy(group.routing_strategy)
-
-            for model_name in group.models:
-                if model_name in self._model_to_group:
-                    raise ValueError(
-                        f"routing_groups: model_name '{model_name}' appears in "
-                        f"both '{self._model_to_group[model_name]}' and "
-                        f"'{group.group_name}'. Each model may belong to at most one group."
-                    )
-                if known_model_names and model_name not in known_model_names:
-                    verbose_router_logger.warning(
-                        "routing_groups: model_name '%s' (group '%s') is not in model_list; "
-                        "the group entry will only take effect once a deployment with that "
-                        "model_name is added.",
-                        model_name,
-                        group.group_name,
-                    )
-                self._model_to_group[model_name] = group.group_name
-
-            self._routing_groups[group.group_name] = group
-
-            strategy_value = self._normalize_strategy(group.routing_strategy) or ""
-            group_selector = self._build_strategy_selector(
-                strategy=group.routing_strategy,
-                routing_strategy_args=group.routing_strategy_args or {},
+        built: Final = tuple(
+            (
+                group,
+                self._build_strategy_selector(
+                    strategy=group.routing_strategy,
+                    routing_strategy_args=group.routing_strategy_args or {},
+                    register_callbacks=False,
+                ),
             )
-            self._group_selectors[group.group_name] = (
-                {strategy_value: group_selector} if group_selector is not None else {}
+            for group in groups
+        )
+        self._replace_routing_groups(built)
+
+    def _replace_routing_groups(
+        self,
+        built: tuple[tuple[RoutingGroup, RouterStrategySelector | None], ...],
+    ) -> None:
+        previous_selectors: Final[Mapping[str, Mapping[str, RouterStrategySelector]]] = getattr(
+            self, "_group_selectors", {}
+        )
+        self._unregister_router_selectors(
+            tuple(sel for selectors in previous_selectors.values() for sel in selectors.values())
+        )
+        for _, selector in built:
+            if selector is not None:
+                self._register_router_selector(selector)
+
+        self._routing_groups: dict[str, RoutingGroup] = {group.group_name: group for group, _ in built}
+        self._model_to_group: dict[str, str] = {
+            model_name: group.group_name for group, _ in built for model_name in group.models
+        }
+        self._group_selectors: dict[str, dict[str, RouterStrategySelector]] = {
+            group.group_name: (
+                {} if selector is None else {self._normalize_strategy(group.routing_strategy) or "": selector}
             )
+            for group, selector in built
+        }
+        self._invalidate_model_group_info_cache()
+        self._invalidate_access_groups_cache()
 
     def get_routing_group(self, model_name: str) -> RoutingGroup | None:
         """
@@ -12032,7 +12021,6 @@ class Router:
                     _casted_value = int(kwargs[var])
                     setattr(self, var, _casted_value)
                 elif var == "routing_groups":
-                    self._routing_groups_input = kwargs[var]
                     rebuild_routing_groups = True
                 elif var == "optional_pre_call_checks":
                     self.set_optional_pre_call_checks(kwargs[var])
@@ -12073,7 +12061,9 @@ class Router:
             self._apply_updated_routing_strategy_args()
 
         if rebuild_routing_groups:
-            self._init_routing_groups(self._routing_groups_input)
+            routing_groups_input: Final = kwargs.get("routing_groups", self._routing_groups_input)
+            self._init_routing_groups(routing_groups_input)
+            self._routing_groups_input = routing_groups_input
         verbose_router_logger.debug("Updated Router settings: %s", self.get_settings())
 
     def _get_client(self, deployment, kwargs, client_type=None):

litellm/router_utils/routing_groups.py

@@ -0,0 +1,95 @@
+"""
+Validation for `router_settings.routing_groups`, shared by the Router and the
+proxy's config-update endpoint so a config the UI saves cannot be one the
+runtime refuses to load.
+"""
+
+from collections.abc import Sequence
+from typing import Final
+
+from litellm._logging import verbose_router_logger
+from litellm.types.router import RoutingGroup, RoutingStrategy
+
+
+def validate_routing_strategy(routing_strategy: RoutingStrategy | str | None) -> None:
+    """
+    Raises `ValueError` unless `routing_strategy` is a known strategy or None.
+
+    See: https://github.com/BerriAI/litellm/issues/11330
+    """
+    if routing_strategy is None:
+        return
+
+    valid_strategy_strings: Final = ("simple-shuffle", "lar1", *(s.value for s in RoutingStrategy))
+    is_valid_string: Final = isinstance(routing_strategy, str) and routing_strategy in valid_strategy_strings
+    is_valid_enum: Final = isinstance(routing_strategy, RoutingStrategy)
+    if not is_valid_string and not is_valid_enum:
+        raise ValueError(
+            f"Invalid routing_strategy: '{routing_strategy}'. "
+            f"Valid options: {list(valid_strategy_strings)}. "
+            f"Check 'router_settings.routing_strategy' in your config.yaml "
+            f"or the 'routing_strategy' parameter if using the Router SDK directly."
+        )
+
+
+def parse_routing_groups(
+    groups_input: Sequence[RoutingGroup | dict] | None,
+    known_model_names: frozenset[str] = frozenset(),
+) -> tuple[RoutingGroup, ...]:
+    """
+    Parses and validates `routing_groups`, raising `ValueError` on the first
+    problem found. Every check runs before the caller mutates any state, so an
+    invalid update can never leave a router holding a half-applied set of
+    groups.
+    """
+    if not groups_input:
+        return ()
+
+    groups: Final = tuple(raw if isinstance(raw, RoutingGroup) else RoutingGroup(**raw) for raw in groups_input)
+
+    if any(not group.group_name for group in groups):
+        raise ValueError("routing_groups: group_name must be non-empty.")
+
+    if any(group.group_name == "default" for group in groups):
+        raise ValueError("routing_groups: 'default' is reserved for the implicit fallback group.")
+
+    names: Final = tuple(group.group_name for group in groups)
+    duplicate_names: Final = frozenset(name for name in names if names.count(name) > 1)
+    if duplicate_names:
+        raise ValueError(f"routing_groups: group names must be unique, duplicate group_name '{min(duplicate_names)}'.")
+
+    for group in groups:
+        validate_routing_strategy(group.routing_strategy)
+
+    owners_by_model: Final = tuple(
+        (model_name, tuple(group.group_name for group in groups if model_name in group.models))
+        for model_name in dict.fromkeys(model_name for group in groups for model_name in group.models)
+    )
+    conflicts: Final = tuple(
+        f"model_name '{model_name}' appears in {' and '.join(repr(owner) for owner in owners)}"
+        for model_name, owners in owners_by_model
+        if len(owners) > 1
+    )
+    if conflicts:
+        raise ValueError(f"routing_groups: {'; '.join(conflicts)}. Each model may belong to at most one group.")
+
+    unknown_models: Final = (
+        tuple(
+            (model_name, group.group_name)
+            for group in groups
+            for model_name in group.models
+            if model_name not in known_model_names
+        )
+        if known_model_names
+        else ()
+    )
+    for model_name, group_name in unknown_models:
+        verbose_router_logger.warning(
+            "routing_groups: model_name '%s' (group '%s') is not in model_list; "
+            "the group entry will only take effect once a deployment with that "
+            "model_name is added.",
+            model_name,
+            group_name,
+        )
+
+    return groups

tests/test_litellm/proxy/test_proxy_server.py

@@ -4959,6 +4959,71 @@ async def test_add_router_settings_from_db_config_merge_logic():
     assert combined_settings["nested_config"] == expected_nested
 
 
+def _routing_groups_router():
+    from litellm import Router
+
+    return Router(
+        model_list=[
+            {"model_name": "m1", "litellm_params": {"model": "openai/gpt-4o", "api_key": "sk-test"}},
+            {"model_name": "m2", "litellm_params": {"model": "openai/gpt-4o-mini", "api_key": "sk-test"}},
+        ],
+        routing_groups=[{"group_name": "g1", "models": ["m1"], "routing_strategy": "latency-based-routing"}],
+    )
+
+
+@pytest.mark.asyncio
+async def test_invalid_db_routing_groups_do_not_abort_other_router_settings():
+    """Regression: an overlapping routing_groups value persisted in DB used to raise out of
+    _add_router_settings_from_db_config, which skipped SSO / guardrail loading downstream."""
+    from unittest.mock import AsyncMock, MagicMock
+
+    from litellm.proxy.proxy_server import ProxyConfig
+
+    router = _routing_groups_router()
+    mock_db_config = MagicMock()
+    mock_db_config.param_value = {
+        "num_retries": 7,
+        "routing_groups": [
+            {"group_name": "g1", "models": ["m1"], "routing_strategy": "latency-based-routing"},
+            {"group_name": "g2", "models": ["m1"], "routing_strategy": "least-busy"},
+        ],
+    }
+    mock_prisma_client = MagicMock()
+    mock_prisma_client.db.litellm_config.find_first = AsyncMock(return_value=mock_db_config)
+
+    await ProxyConfig()._add_router_settings_from_db_config(
+        config_data={}, llm_router=router, prisma_client=mock_prisma_client
+    )
+
+    assert router.num_retries == 7
+    assert router._model_to_group == {"m1": "g1"}
+    assert router._get_routing_context("m1", None)[0] == "latency-based-routing"
+
+
+@pytest.mark.asyncio
+async def test_valid_db_routing_groups_still_replace_router_groups():
+    from unittest.mock import AsyncMock, MagicMock
+
+    from litellm.proxy.proxy_server import ProxyConfig
+
+    router = _routing_groups_router()
+    mock_db_config = MagicMock()
+    mock_db_config.param_value = {
+        "num_retries": 7,
+        "routing_groups": [{"group_name": "g2", "models": ["m2"], "routing_strategy": "least-busy"}],
+    }
+    mock_prisma_client = MagicMock()
+    mock_prisma_client.db.litellm_config.find_first = AsyncMock(return_value=mock_db_config)
+
+    await ProxyConfig()._add_router_settings_from_db_config(
+        config_data={}, llm_router=router, prisma_client=mock_prisma_client
+    )
+
+    assert router.num_retries == 7
+    assert router._model_to_group == {"m2": "g2"}
+    assert router._get_routing_context("m2", None)[0] == "least-busy"
+
+
 @pytest.mark.asyncio
 async def test_add_router_settings_from_db_config_empty_db_lists_do_not_clobber_config_fallbacks():
     """
@@ -9224,6 +9289,52 @@ def test_update_config_writes_only_sent_section(_update_config_setup):
         restore()
 
 
+def test_update_config_rejects_overlapping_routing_groups_before_writing(_update_config_setup):
+    """Regression: overlapping groups were persisted and only failed at router reload, where the
+    failure took SSO and the other DB-backed settings down with it."""
+    existing_groups = [{"group_name": "g1", "models": ["m1"], "routing_strategy": "least-busy"}]
+    client, prisma, restore = _update_config_setup(
+        initial_rows={"router_settings": {"num_retries": 2, "routing_groups": existing_groups}}
+    )
+    try:
+        resp = client.post(
+            "/config/update",
+            json={
+                "router_settings": {
+                    "routing_groups": [
+                        *existing_groups,
+                        {"group_name": "g2", "models": ["m1"], "routing_strategy": "latency-based-routing"},
+                    ]
+                }
+            },
+        )
+        assert resp.status_code == 400
+        assert "'m1' appears in 'g1' and 'g2'" in resp.text
+        assert prisma.db.litellm_config.upsert_calls == []
+        assert prisma.db.litellm_config.rows["router_settings"]["routing_groups"] == existing_groups
+    finally:
+        restore()
+
+
+def test_update_config_accepts_disjoint_routing_groups(_update_config_setup):
+    client, prisma, restore = _update_config_setup(initial_rows={"router_settings": {"num_retries": 2}})
+    groups = [
+        {"group_name": "g1", "models": ["m1"], "routing_strategy": "least-busy"},
+        {"group_name": "g2", "models": ["m2"], "routing_strategy": "latency-based-routing"},
+    ]
+    try:
+        resp = client.post("/config/update", json={"router_settings": {"routing_groups": groups}})
+        assert resp.status_code == 200
+        stored = prisma.db.litellm_config.rows["router_settings"]
+        assert stored["num_retries"] == 2
+        assert [(g["group_name"], g["models"]) for g in stored["routing_groups"]] == [
+            ("g1", ["m1"]),
+            ("g2", ["m2"]),
+        ]
+    finally:
+        restore()
+
+
 def test_update_config_env_var_round_trip_not_double_encrypted(_update_config_setup, monkeypatch):
     """Endpoint-level regression for the /config/update double-encryption bug.
 

tests/test_litellm/router_strategy/test_router_routing_groups.py

@@ -13,6 +13,7 @@ from collections.abc import Callable
 from unittest.mock import patch
 
 import pytest
+from pydantic import ValidationError
 
 import litellm
 from litellm import Router
@@ -806,6 +807,118 @@ def test_strategy_reinit_unregisters_override_selectors():
     assert router._get_override_strategy_selector("latency-based-routing") is router.lowestlatency_logger
 
 
+def _single_latency_group():
+    return [{"group_name": "g1", "models": ["filtered-model"], "routing_strategy": "latency-based-routing"}]
+
+
+def _assert_still_routes_with_original_group(router, selector):
+    assert list(router._routing_groups) == ["g1"]
+    assert router._model_to_group == {"filtered-model": "g1"}
+    assert router._group_selectors["g1"]["latency-based-routing"] is selector
+    assert router._get_routing_context("filtered-model", None) == ("latency-based-routing", selector)
+    assert sum(1 for cb in litellm.callbacks if cb is selector) == 1
+
+
+def test_failed_routing_groups_update_keeps_previous_groups(monkeypatch):
+    monkeypatch.setattr(litellm, "callbacks", [])
+    monkeypatch.setattr(litellm, "input_callback", [])
+    router = _build_router(routing_groups=_single_latency_group())
+    selector = router._group_selectors["g1"]["latency-based-routing"]
+
+    with pytest.raises(ValueError, match="appears in"):
+        router.update_settings(
+            routing_groups=[
+                *_single_latency_group(),
+                {"group_name": "g2", "models": ["filtered-model"], "routing_strategy": "least-busy"},
+            ],
+        )
+
+    _assert_still_routes_with_original_group(router, selector)
+    assert sum(1 for cb in litellm.callbacks if type(cb) is not type(selector)) == 0
+    assert litellm.input_callback == []
+
+
+def test_failed_routing_groups_update_does_not_poison_later_strategy_changes(monkeypatch):
+    monkeypatch.setattr(litellm, "callbacks", [])
+    monkeypatch.setattr(litellm, "input_callback", [])
+    router = _build_router(routing_groups=_single_latency_group())
+
+    with pytest.raises(ValueError, match="appears in"):
+        router.update_settings(
+            routing_groups=[
+                *_single_latency_group(),
+                {"group_name": "g2", "models": ["filtered-model"], "routing_strategy": "least-busy"},
+            ],
+        )
+
+    router.update_settings(routing_strategy="least-busy")
+
+    assert list(router._routing_groups) == ["g1"]
+    assert [g["group_name"] for g in router.get_settings()["routing_groups"]] == ["g1"]
+
+
+def test_overlap_error_names_every_conflicting_model():
+    with pytest.raises(ValueError, match="appears in") as exc_info:
+        _build_router(
+            routing_groups=[
+                {
+                    "group_name": "g1",
+                    "models": ["filtered-model", "other-model"],
+                    "routing_strategy": "latency-based-routing",
+                },
+                {
+                    "group_name": "g2",
+                    "models": ["filtered-model", "other-model"],
+                    "routing_strategy": "least-busy",
+                },
+            ],
+        )
+    message = str(exc_info.value)
+    assert "'filtered-model' appears in 'g1' and 'g2'" in message
+    assert "'other-model' appears in 'g1' and 'g2'" in message
+
+
+def test_invalid_group_strategy_keeps_previous_groups(monkeypatch):
+    monkeypatch.setattr(litellm, "callbacks", [])
+    monkeypatch.setattr(litellm, "input_callback", [])
+    router = _build_router(routing_groups=_single_latency_group())
+    selector = router._group_selectors["g1"]["latency-based-routing"]
+
+    with pytest.raises(ValueError, match="Invalid routing_strategy"):
+        router.update_settings(
+            routing_groups=[
+                {"group_name": "g2", "models": ["other-model"], "routing_strategy": "not-a-real-strategy"},
+            ],
+        )
+
+    _assert_still_routes_with_original_group(router, selector)
+
+
+def test_unbuildable_group_selector_keeps_previous_groups(monkeypatch):
+    monkeypatch.setattr(litellm, "callbacks", [])
+    monkeypatch.setattr(litellm, "input_callback", [])
+    router = _build_router(routing_groups=_single_latency_group())
+    selector = router._group_selectors["g1"]["latency-based-routing"]
+
+    with pytest.raises(ValidationError, match="ttl"):
+        router.update_settings(
+            routing_groups=[
+                {"group_name": "g0", "models": ["other-model"], "routing_strategy": "least-busy"},
+                *_single_latency_group(),
+                {
+                    "group_name": "g2",
+                    "models": ["other-model-2"],
+                    "routing_strategy": "latency-based-routing",
+                    "routing_strategy_args": {"ttl": "not-a-number"},
+                },
+            ],
+        )
+
+    _assert_still_routes_with_original_group(router, selector)
+    assert litellm.callbacks == [selector]
+    assert litellm.input_callback == []
+
+
 def test_override_selectors_are_not_registered_process_wide(monkeypatch):
     monkeypatch.setattr(litellm, "callbacks", [])
     monkeypatch.setattr(litellm, "input_callback", [])

ui/litellm-dashboard/src/components/routing_groups/RoutingGroupModal.test.tsx

@@ -59,6 +59,7 @@ const renderModal = (overrides: Partial<React.ComponentProps<typeof RoutingGroup
       strategyDescriptions={STRATEGY_DESCRIPTIONS}
       modelOptions={MODEL_OPTIONS}
       existingGroupNames={["already-taken", "other-group"]}
+      groupNameByModel={{}}
       onClose={onClose}
       onSubmit={onSubmit}
       {...overrides}
@@ -307,6 +308,19 @@ describe("RoutingGroupModal", () => {
     expect(onSubmit.mock.calls[0][0]).toStrictEqual(expected);
   });
 
+  it("blocks a model another group already claims", async () => {
+    const user = userEvent.setup();
+    const { onSubmit } = renderModal({ groupNameByModel: { "gpt-4o": "cheap" } });
+
+    await typeName(user, "security");
+    await pickModels(user, "gpt-4o");
+    await pickStrategy(user, "latency-based-routing");
+    await save(user, "Create Group");
+
+    expect(await screen.findByText(/Already claimed: gpt-4o/)).toBeInTheDocument();
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
   it("describes the selected strategy", async () => {
     renderModal();
 

ui/litellm-dashboard/src/components/routing_groups/RoutingGroupModal.tsx

@@ -29,6 +29,7 @@ import {
   toRoutingGroupFormValues,
 } from "./routingGroupPayload";
 import type { RoutingGroup } from "./types";
+import { modelConflictError } from "./modelOwnership";
 import { Dialog, DialogContent, DialogFooter, DialogHeader, DialogTitle } from "@/components/ui/dialog";
 import { Button } from "@/components/ui/button";
 
@@ -40,6 +41,7 @@ interface RoutingGroupModalProps {
   strategyDescriptions: Record<string, string>;
   modelOptions: string[];
   existingGroupNames: string[];
+  groupNameByModel: Record<string, string>;
   onClose: () => void;
   onSubmit: (group: RoutingGroup) => Promise<void> | void;
   saving?: boolean;
@@ -57,6 +59,7 @@ const RoutingGroupModal: React.FC<RoutingGroupModalProps> = ({
   strategyDescriptions,
   modelOptions,
   existingGroupNames,
+  groupNameByModel,
   onClose,
   onSubmit,
   saving,
@@ -77,12 +80,20 @@ const RoutingGroupModal: React.FC<RoutingGroupModalProps> = ({
         .min(1, "Group name is required")
         .max(GROUP_NAME_MAX_LENGTH, `Must be ${GROUP_NAME_MAX_LENGTH} characters or fewer`)
         .refine((value) => !reservedNames.has(value.toLowerCase()), "A group with this name already exists"),
-      models: z.array(z.string()).min(1, "Select at least one model"),
+      models: z
+        .array(z.string())
+        .min(1, "Select at least one model")
+        .superRefine((models, ctx) => {
+          const conflict = modelConflictError(models, groupNameByModel);
+          if (conflict !== null) {
+            ctx.addIssue({ code: "custom", message: conflict });
+          }
+        }),
       routing_strategy: z.string().min(1, "Strategy is required"),
       routing_strategy_args: z.string(),
     };
     return z.object(shape);
-  }, [reservedNames]);
+  }, [reservedNames, groupNameByModel]);
 
   const form = useZodForm(schema, { defaultValues: toRoutingGroupFormValues(initialValue, availableStrategies) });
 
@@ -124,7 +135,7 @@ const RoutingGroupModal: React.FC<RoutingGroupModalProps> = ({
               control={form.control}
               name="models"
               label="Models"
-              description="Models from your model list that this group routes between."
+              description="Models from your model list that this group routes between. A model can only be in one group."
             >
               {({ id, value, onChange, "aria-invalid": ariaInvalid, "aria-describedby": ariaDescribedBy }) => (
                 <Combobox multiple items={modelOptions} value={value} onValueChange={onChange}>

ui/litellm-dashboard/src/components/routing_groups/index.tsx

@@ -14,6 +14,7 @@ import RoutingGroupsTable from "./RoutingGroupsTable";
 import RoutingGroupModal from "./RoutingGroupModal";
 import { toast } from "@/lib/toast";
 import type { RoutingGroup } from "./types";
+import { groupNameByModel } from "./modelOwnership";
 import { Dialog, DialogContent, DialogFooter, DialogHeader, DialogTitle } from "@/components/ui/dialog";
 
 const RoutingGroups: React.FC = () => {
@@ -30,7 +31,7 @@ const RoutingGroups: React.FC = () => {
   const [editingGroup, setEditingGroup] = useState<RoutingGroup | null>(null);
   const [deletingGroup, setDeletingGroup] = useState<RoutingGroup | null>(null);
 
-  const groups = data?.routingGroups ?? [];
+  const groups = useMemo(() => data?.routingGroups ?? [], [data?.routingGroups]);
 
   const filteredGroups = useMemo(() => {
     const q = searchQuery.trim().toLowerCase();
@@ -51,6 +52,11 @@ const RoutingGroups: React.FC = () => {
 
   const strategyDescriptions = routerFields?.routing_strategy_descriptions ?? {};
 
+  const ownerByModel = useMemo(
+    () => groupNameByModel(groups, drawerMode === "edit" ? editingGroup?.group_name : undefined),
+    [groups, drawerMode, editingGroup],
+  );
+
   const modelOptions = useMemo<string[]>(() => {
     const records = (modelHub?.data ?? []) as Array<{ model_group?: string }>;
     const names = records.map((r) => r.model_group).filter((n): n is string => Boolean(n));
@@ -160,6 +166,7 @@ const RoutingGroups: React.FC = () => {
         strategyDescriptions={strategyDescriptions}
         modelOptions={modelOptions}
         existingGroupNames={groups.map((g) => g.group_name)}
+        groupNameByModel={ownerByModel}
         onClose={() => setDrawerOpen(false)}
         onSubmit={handleSubmit}
         saving={saveMutation.isPending}

ui/litellm-dashboard/src/components/routing_groups/modelOwnership.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+
+import { groupNameByModel, modelConflictError } from "./modelOwnership";
+import type { RoutingGroup } from "./types";
+
+const groups: RoutingGroup[] = [
+  { group_name: "cheap", models: ["m1", "m2"], routing_strategy: "latency-based-routing" },
+  { group_name: "security", models: ["m3"], routing_strategy: "least-busy" },
+];
+
+describe("groupNameByModel", () => {
+  it("maps every claimed model to its owning group", () => {
+    expect(groupNameByModel(groups)).toEqual({ m1: "cheap", m2: "cheap", m3: "security" });
+  });
+
+  it("excludes the group being edited so its own models stay selectable", () => {
+    expect(groupNameByModel(groups, "cheap")).toEqual({ m3: "security" });
+  });
+});
+
+describe("modelConflictError", () => {
+  it("passes models that no other group claims", () => {
+    expect(modelConflictError(["m4"], groupNameByModel(groups, "cheap"))).toBeNull();
+    expect(modelConflictError(undefined, groupNameByModel(groups))).toBeNull();
+  });
+
+  it("names every model already claimed by another group", () => {
+    const error = modelConflictError(["m1", "m3", "m4"], groupNameByModel(groups));
+    expect(error).toBe(
+      'Each model may belong to at most one group. Already claimed: m1 (in "cheap"), m3 (in "security")',
+    );
+  });
+});

ui/litellm-dashboard/src/components/routing_groups/modelOwnership.ts

@@ -0,0 +1,18 @@
+import type { RoutingGroup } from "./types";
+
+export const groupNameByModel = (groups: RoutingGroup[], excludeGroupName?: string): Record<string, string> =>
+  Object.fromEntries(
+    groups
+      .filter((group) => group.group_name !== excludeGroupName)
+      .flatMap((group) => group.models.map((model) => [model, group.group_name] as const)),
+  );
+
+export const modelConflictError = (
+  models: string[] | undefined,
+  ownerByModel: Record<string, string>,
+): string | null => {
+  const conflicts = (models ?? []).filter((model) => ownerByModel[model] !== undefined);
+  if (conflicts.length === 0) return null;
+  const detail = conflicts.map((model) => `${model} (in "${ownerByModel[model]}")`).join(", ");
+  return `Each model may belong to at most one group. Already claimed: ${detail}`;
+};