diff --git a/litellm/vector_stores/vector_store_registry.py b/litellm/vector_stores/vector_store_registry.py
index e78d2aa5f6a..6a6668119b5 100644
--- a/litellm/vector_stores/vector_store_registry.py
+++ b/litellm/vector_stores/vector_store_registry.py
@@ -32,8 +32,10 @@ else:
 
 
 class VectorStoreIndexRegistry:
-    def __init__(self, vector_store_indexes: list[LiteLLM_ManagedVectorStoreIndex] = []):
-        self.vector_store_indexes: list[LiteLLM_ManagedVectorStoreIndex] = vector_store_indexes
+    def __init__(self, vector_store_indexes: list[LiteLLM_ManagedVectorStoreIndex] | None = None):
+        self.vector_store_indexes: list[LiteLLM_ManagedVectorStoreIndex] = (
+            vector_store_indexes if vector_store_indexes is not None else []
+        )
 
     def get_vector_store_indexes(self) -> list[LiteLLM_ManagedVectorStoreIndex]:
         """
@@ -101,8 +103,8 @@ class VectorStoreIndexRegistry:
 
 
 class VectorStoreRegistry:
-    def __init__(self, vector_stores: list[LiteLLM_ManagedVectorStore] = []):
-        self.vector_stores: list[LiteLLM_ManagedVectorStore] = vector_stores
+    def __init__(self, vector_stores: list[LiteLLM_ManagedVectorStore] | None = None):
+        self.vector_stores: list[LiteLLM_ManagedVectorStore] = vector_stores if vector_stores is not None else []
         self.vector_store_ids_to_vector_store_map: dict[str, LiteLLM_ManagedVectorStore] = {}
 
     def _extract_tool_params(self, tool: dict) -> VectorStoreToolParams:
diff --git a/tests/unit/vector_stores/test_vector_store_registry.py b/tests/unit/vector_stores/test_vector_store_registry.py
index 762176d6a81..f435b1e7630 100644
--- a/tests/unit/vector_stores/test_vector_store_registry.py
+++ b/tests/unit/vector_stores/test_vector_store_registry.py
@@ -8,12 +8,20 @@ from fastapi.testclient import TestClient
 
 
 from datetime import datetime, timezone
+from typing import Final
 from unittest.mock import AsyncMock, MagicMock
 
 import litellm
-from litellm.types.vector_stores import LiteLLM_ManagedVectorStore
+from litellm.types.vector_stores import (
+    IndexCreateLiteLLMParams,
+    LiteLLM_ManagedVectorStore,
+    LiteLLM_ManagedVectorStoreIndex,
+)
 from litellm.vector_stores.main import search
-from litellm.vector_stores.vector_store_registry import VectorStoreRegistry
+from litellm.vector_stores.vector_store_registry import (
+    VectorStoreIndexRegistry,
+    VectorStoreRegistry,
+)
 
 
 @pytest.fixture(autouse=True)
@@ -249,3 +257,41 @@ async def test_config_owned_store_survives_db_liveness_check_while_missing_db_st
     prisma_client.db.litellm_managedvectorstorestable.find_unique.assert_awaited_once_with(
         where={"vector_store_id": "vs_from_db"}
     )
+
+
+class TestRegistriesDoNotShareDefaultState:
+    """#38874: default-constructed registries must not share one list."""
+
+    def test_vector_store_registries_do_not_share_a_list(self):
+        first: Final = VectorStoreRegistry()
+        second: Final = VectorStoreRegistry()
+        assert first.vector_stores is not second.vector_stores
+
+    def test_index_registries_do_not_share_a_list(self):
+        first: Final = VectorStoreIndexRegistry()
+        second: Final = VectorStoreIndexRegistry()
+        assert first.vector_store_indexes is not second.vector_store_indexes
+
+    def test_adding_to_one_registry_leaves_the_next_one_empty(self):
+        VectorStoreRegistry().add_vector_store_to_registry(
+            LiteLLM_ManagedVectorStore(vector_store_id="vs-leak", custom_llm_provider="bedrock")
+        )
+        assert VectorStoreRegistry().vector_stores == []
+
+    def test_upserting_into_one_index_registry_leaves_the_next_one_empty(self):
+        VectorStoreIndexRegistry().upsert_vector_store_index(
+            LiteLLM_ManagedVectorStoreIndex(
+                id="idx-leak",
+                index_name="leak",
+                litellm_params=IndexCreateLiteLLMParams(vector_store_index="vs-leak", vector_store_name="leak"),
+            )
+        )
+        assert VectorStoreIndexRegistry().get_vector_store_indexes() == []
+
+    def test_a_supplied_list_is_still_used_as_given(self):
+        supplied: Final = [LiteLLM_ManagedVectorStore(vector_store_id="vs-1", custom_llm_provider="bedrock")]
+        assert VectorStoreRegistry(vector_stores=supplied).vector_stores is supplied
+
+    def test_a_supplied_empty_list_is_still_used_as_given(self):
+        supplied: Final[list[LiteLLM_ManagedVectorStore]] = []
+        assert VectorStoreRegistry(vector_stores=supplied).vector_stores is supplied