diff --git a/backend/open_webui/main.py b/backend/open_webui/main.py
index 57660fe9e4..b95166a9fd 100644
--- a/backend/open_webui/main.py
+++ b/backend/open_webui/main.py
@@ -1760,9 +1760,9 @@ async def chat_completion(
                 "local:"
             ):  # temporary chats are not stored
 
-                # Verify chat ownership
-                chat = Chats.get_chat_by_id_and_user_id(metadata["chat_id"], user.id)
-                if chat is None and user.role != "admin":  # admins can access any chat
+                # Verify chat ownership — lightweight EXISTS check avoids
+                # deserializing the full chat JSON blob just to confirm the row exists
+                if not Chats.is_chat_owner(metadata["chat_id"], user.id) and user.role != "admin":  # admins can access any chat
                     raise HTTPException(
                         status_code=status.HTTP_404_NOT_FOUND,
                         detail=ERROR_MESSAGES.DEFAULT(),
diff --git a/backend/open_webui/models/chats.py b/backend/open_webui/models/chats.py
index 42c8cb4508..84c67a5b15 100644
--- a/backend/open_webui/models/chats.py
+++ b/backend/open_webui/models/chats.py
@@ -974,6 +974,41 @@ class ChatTable:
         except Exception:
             return None
 
+    def is_chat_owner(
+        self, id: str, user_id: str, db: Optional[Session] = None
+    ) -> bool:
+        """
+        Lightweight ownership check — uses EXISTS subquery instead of loading
+        the full Chat row (which includes the potentially large JSON blob).
+        """
+        try:
+            with get_db_context(db) as db:
+                return db.query(
+                    exists().where(
+                        and_(Chat.id == id, Chat.user_id == user_id)
+                    )
+                ).scalar()
+        except Exception:
+            return False
+
+    def get_chat_folder_id(
+        self, id: str, user_id: str, db: Optional[Session] = None
+    ) -> Optional[str]:
+        """
+        Fetch only the folder_id column for a chat, without loading the full
+        JSON blob. Returns None if chat doesn't exist or doesn't belong to user.
+        """
+        try:
+            with get_db_context(db) as db:
+                result = (
+                    db.query(Chat.folder_id)
+                    .filter_by(id=id, user_id=user_id)
+                    .first()
+                )
+                return result[0] if result else None
+        except Exception:
+            return None
+
     def get_chats(
         self, skip: int = 0, limit: int = 50, db: Optional[Session] = None
     ) -> list[ChatModel]:
diff --git a/backend/open_webui/utils/middleware.py b/backend/open_webui/utils/middleware.py
index c2b2b07cb1..218deed17e 100644
--- a/backend/open_webui/utils/middleware.py
+++ b/backend/open_webui/utils/middleware.py
@@ -2078,11 +2078,12 @@ async def process_chat_payload(request, form_data, user, metadata, model):
 
     # Folder "Project" handling
     # Check if the request has chat_id and is inside of a folder
+    # Uses lightweight column query — only fetches folder_id, not the full chat JSON blob
     chat_id = metadata.get("chat_id", None)
     if chat_id and user:
-        chat = Chats.get_chat_by_id_and_user_id(chat_id, user.id)
-        if chat and chat.folder_id:
-            folder = Folders.get_folder_by_id_and_user_id(chat.folder_id, user.id)
+        folder_id = Chats.get_chat_folder_id(chat_id, user.id)
+        if folder_id:
+            folder = Folders.get_folder_by_id_and_user_id(folder_id, user.id)
 
             if folder and folder.data:
                 if "system_prompt" in folder.data: