fix: prevent sentinel from leaking into /v1/models API response (#23850)

The fail-closed sentinel "__access_group_no_models__" was passing
through get_complete_model_list() unchanged and reaching callers that
return model lists directly to end-users, causing it to appear as a
model ID in GET /v1/models responses.

- Extract sentinel to named constant ACCESS_GROUP_NO_MODELS_SENTINEL
  in model_checks.py so all references stay in sync
- Strip the sentinel from all_models before returning in utils.py
- Strip it from all_models_str in proxy_server.py as a safety net

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

litellm/proxy/auth/model_checks.py

@@ -132,6 +132,13 @@ def get_key_models(
     return all_models
 
 
+# Sentinel used by get_key_models_with_db_access_groups to signal "key has
+# access_group_ids but none resolved to any model" so that get_complete_model_list()
+# does not fall through to team_models (fail-closed).  Callers that return model
+# lists to end-users MUST strip this value before responding.
+ACCESS_GROUP_NO_MODELS_SENTINEL = "__access_group_no_models__"
+
+
 async def get_key_models_with_db_access_groups(
     user_api_key_dict: UserAPIKeyAuth,
     proxy_model_list: List[str],
@@ -168,7 +175,7 @@ async def get_key_models_with_db_access_groups(
         # Fail-closed: if the access group is configured but resolves to nothing
         # (deleted group, DB unavailable, or empty group), use a sentinel so
         # get_complete_model_list() does NOT fall through to team_models.
-        key_models = db_models if db_models else ["__access_group_no_models__"]
+        key_models = db_models if db_models else [ACCESS_GROUP_NO_MODELS_SENTINEL]
 
     return key_models
 

litellm/proxy/proxy_server.py

@@ -275,6 +275,7 @@ from litellm.proxy.auth.auth_utils import check_response_size_is_safe
 from litellm.proxy.auth.handle_jwt import JWTHandler
 from litellm.proxy.auth.litellm_license import LicenseCheck
 from litellm.proxy.auth.model_checks import (
+    ACCESS_GROUP_NO_MODELS_SENTINEL,
     get_all_fallbacks,
     get_complete_model_list,
     get_key_models,
@@ -10871,6 +10872,8 @@ async def model_info_v1(  # noqa: PLR0915
         infer_model_from_keys=general_settings.get("infer_model_from_keys", False),
         llm_router=llm_router,
     )
+    # Strip the fail-closed sentinel — it must never appear in the /v1/models response.
+    all_models_str = [m for m in all_models_str if m != ACCESS_GROUP_NO_MODELS_SENTINEL]
 
     if len(all_models_str) > 0:
         _relevant_models = []

litellm/proxy/utils.py

@@ -5516,6 +5516,7 @@ async def get_available_models_for_user(
     """
     from litellm.proxy.auth.auth_checks import get_team_object
     from litellm.proxy.auth.model_checks import (
+        ACCESS_GROUP_NO_MODELS_SENTINEL,
         get_complete_model_list,
         get_key_models_with_db_access_groups,
         get_team_models,
@@ -5581,6 +5582,10 @@ async def get_available_models_for_user(
         only_model_access_groups=only_model_access_groups,
     )
 
+    # Strip the fail-closed sentinel before returning to callers — it must never
+    # appear in a model listing response (e.g. GET /v1/models).
+    all_models = [m for m in all_models if m != ACCESS_GROUP_NO_MODELS_SENTINEL]
+
     return all_models