diff --git a/litellm/vector_stores/vector_store_registry.py b/litellm/vector_stores/vector_store_registry.py
index 2bac8921d5f..520edc06548 100644
--- a/litellm/vector_stores/vector_store_registry.py
+++ b/litellm/vector_stores/vector_store_registry.py
@@ -376,16 +376,15 @@ class VectorStoreRegistry:
         return vector_stores_to_run
 
     def _get_vector_store_ids_from_tool_calls(
-        self, tools: Optional[List[Dict]] = None, vector_store_ids: List[str] = []
+        self, tools: Optional[List[Dict]] = None, vector_store_ids: Optional[List[str]] = None
     ) -> List[str]:
         """
         Returns the vector store ids from the tool calls
         """
-        if tools:
-            for tool in tools:
-                if "vector_store_ids" in tool:
-                    vector_store_ids.extend(tool["vector_store_ids"])
-        return vector_store_ids
+        return [
+            *(vector_store_ids or ()),
+            *(vs_id for tool in (tools or ()) if "vector_store_ids" in tool for vs_id in tool["vector_store_ids"]),
+        ]
 
     def load_vector_stores_from_config(self, vector_stores_config: List[Dict]):
         """
diff --git a/tests/test_litellm/vector_stores/test_vector_store_registry.py b/tests/test_litellm/vector_stores/test_vector_store_registry.py
index ea3b9e6d42d..d9337d32c13 100644
--- a/tests/test_litellm/vector_stores/test_vector_store_registry.py
+++ b/tests/test_litellm/vector_stores/test_vector_store_registry.py
@@ -279,3 +279,25 @@ def test_delete_vector_store_index_removes_by_name():
 
     registry.delete_vector_store_index("idx_does_not_exist")
     assert [index.index_name for index in registry.vector_store_indexes] == ["idx_b"]
+
+
+def test_get_vector_store_ids_from_tool_calls_does_not_share_or_mutate():
+    """
+    Regression test: _get_vector_store_ids_from_tool_calls took `vector_store_ids: List[str] = []`
+    and extended it in place, so the def-time default accumulated ids across every call that
+    omitted the argument, and a caller-supplied list was mutated behind the caller's back.
+    """
+    registry = VectorStoreRegistry()
+    tools = [{"vector_store_ids": ["vs_a"]}]
+
+    first = registry._get_vector_store_ids_from_tool_calls(tools=tools)
+    second = registry._get_vector_store_ids_from_tool_calls(tools=tools)
+
+    assert first == ["vs_a"]
+    assert second == ["vs_a"]
+
+    caller_ids = ["vs_seed"]
+    result = registry._get_vector_store_ids_from_tool_calls(tools=tools, vector_store_ids=caller_ids)
+
+    assert result == ["vs_seed", "vs_a"]
+    assert caller_ids == ["vs_seed"]