diff --git a/backend/open_webui/config.py b/backend/open_webui/config.py
index 365544e80c..0508580499 100644
--- a/backend/open_webui/config.py
+++ b/backend/open_webui/config.py
@@ -1640,6 +1640,15 @@ DEFAULT_MODELS = os.getenv('DEFAULT_MODELS', None)
 
 DEFAULT_PINNED_MODELS = os.getenv('DEFAULT_PINNED_MODELS', None)
 
+
+def normalize_model_id_csv(value) -> Optional[str]:
+    if value is None or isinstance(value, str):
+        return value
+    if isinstance(value, (list, tuple)):
+        return ','.join(str(model_id).strip() for model_id in value if model_id)
+    return None
+
+
 try:
     default_prompt_suggestions = JSONCodec.loads(os.getenv('DEFAULT_PROMPT_SUGGESTIONS', '[]'))
 except Exception as e:
diff --git a/backend/open_webui/main.py b/backend/open_webui/main.py
index f5c182eb3f..27493c919c 100644
--- a/backend/open_webui/main.py
+++ b/backend/open_webui/main.py
@@ -67,6 +67,7 @@ from open_webui.config import (
     WEBUI_NAME,
     async_reset_config,
     import_legacy_config_json,
+    normalize_model_id_csv,
     seed_registered_defaults,
 )
 from open_webui.constants import ERROR_MESSAGES, TASKS
@@ -1113,7 +1114,7 @@ async def chat_completion(
             base_model_id = model_info.base_model_id
             if base_model_id not in request.app.state.MODELS:
                 if ENABLE_CUSTOM_MODEL_FALLBACK:
-                    default_models = ((await Config.get('ui.default_models')) or '').split(',')
+                    default_models = (normalize_model_id_csv(await Config.get('ui.default_models')) or '').split(',')
 
                     fallback_model_id = default_models[0].strip() if default_models[0] else None
 
@@ -2234,8 +2235,8 @@ async def get_app_config(request: Request):
         },
         **(
             {
-                'default_models': config.get('ui.default_models'),
-                'default_pinned_models': config.get('ui.default_pinned_models'),
+                'default_models': normalize_model_id_csv(config.get('ui.default_models')),
+                'default_pinned_models': normalize_model_id_csv(config.get('ui.default_pinned_models')),
                 'default_prompt_suggestions': config.get('ui.prompt_suggestions'),
                 **({'user_count': user_count} if user_count is not None else {}),
                 'code': {
diff --git a/backend/open_webui/routers/configs.py b/backend/open_webui/routers/configs.py
index f591908a6d..ac96ca4025 100644
--- a/backend/open_webui/routers/configs.py
+++ b/backend/open_webui/routers/configs.py
@@ -7,7 +7,7 @@ from typing import Optional
 import aiohttp
 from fastapi import APIRouter, Depends, HTTPException, Request
 from mcp.shared.auth import OAuthMetadata
-from open_webui.config import BannerModel
+from open_webui.config import BannerModel, normalize_model_id_csv
 from open_webui.env import AIOHTTP_CLIENT_SESSION_SSL, AIOHTTP_CLIENT_TIMEOUT
 from open_webui.events import EVENTS, publish_event
 from open_webui.models.config import Config
@@ -740,15 +740,22 @@ async def get_models_defaults(request: Request, user=Depends(get_verified_user))
     }
 
 
+def normalize_models_config_values(values: dict) -> dict:
+    for field in ('DEFAULT_MODELS', 'DEFAULT_PINNED_MODELS'):
+        if field in values:
+            values[field] = normalize_model_id_csv(values[field])
+    return values
+
+
 @router.get('/models', response_model=ModelsConfigForm)
 async def get_models_config(request: Request, user=Depends(get_admin_user)):
-    return await get_config_values(MODELS_CONFIG_KEYS)
+    return normalize_models_config_values(await get_config_values(MODELS_CONFIG_KEYS))
 
 
 @router.post('/models', response_model=ModelsConfigForm)
 async def set_models_config(request: Request, form_data: ModelsConfigForm, user=Depends(get_admin_user)):
     await Config.upsert(config_updates(form_data.model_dump(), MODELS_CONFIG_KEYS))
-    values = await get_config_values(MODELS_CONFIG_KEYS)
+    values = normalize_models_config_values(await get_config_values(MODELS_CONFIG_KEYS))
     await publish_event(
         request,
         EVENTS.CONFIG_MODELS_UPDATED,