diff --git a/backend/open_webui/retrieval/vector/utils.py b/backend/open_webui/retrieval/vector/utils.py
index 31b5b0748c..85c96e14cb 100644
--- a/backend/open_webui/retrieval/vector/utils.py
+++ b/backend/open_webui/retrieval/vector/utils.py
@@ -6,11 +6,21 @@ from open_webui.utils.misc import sanitize_text_for_db
 
 KEYS_TO_EXCLUDE = ['content', 'pages', 'tables', 'paragraphs', 'sections', 'figures']
 
+# A nested metadata value is deep-copied onto every chunk by the text splitter and then
+# stringified by process_metadata before storage, so a single unbounded one costs memory
+# proportional to the chunk count. KEYS_TO_EXCLUDE only catches the field names we know
+# about; this bounds the ones we do not.
+MAX_NESTED_METADATA_ITEMS = 64
+
+
+def _is_unbounded(value: Any) -> bool:
+    # len() is O(1) for list and dict - never serialize a value just to measure it.
+    return isinstance(value, (list, dict)) and len(value) > MAX_NESTED_METADATA_ITEMS
+
 
 def filter_metadata(metadata: dict[str, any]) -> dict[str, any]:
     # Removes large/redundant fields from metadata dict.
-    metadata = {key: value for key, value in metadata.items() if key not in KEYS_TO_EXCLUDE}
-    return metadata
+    return {key: value for key, value in metadata.items() if key not in KEYS_TO_EXCLUDE and not _is_unbounded(value)}
 
 
 def process_metadata(
@@ -21,7 +31,7 @@ def process_metadata(
     result = {}
     for key, value in metadata.items():
         # Skip large fields
-        if key in KEYS_TO_EXCLUDE:
+        if key in KEYS_TO_EXCLUDE or _is_unbounded(value):
             continue
         if value is None:
             continue