diff --git a/src/lightspeed_rag_content/document_processor.py b/src/lightspeed_rag_content/document_processor.py
index 557da8c..90e09a0 100644
--- a/src/lightspeed_rag_content/document_processor.py
+++ b/src/lightspeed_rag_content/document_processor.py
@@ -540,10 +540,11 @@ async def upload_file(chunk_indices: list[int]) -> str:
                 )
                 embedding = embedding_response.data[0].embedding
 
+                metadata = {**doc.get("metadata", {}), "source": index}
                 chunk = {
                     "content": doc["content"],
                     "chunk_id": doc["chunk_id"],
-                    "metadata": doc.get("metadata", {}),
+                    "metadata": metadata,
                     "chunk_metadata": doc["chunk_metadata"],
                     "embedding": embedding,
                     "embedding_model": embedding_model,
@@ -613,6 +614,7 @@ async def _upload_and_process_files(  # noqa: C901  # pylint: disable=R0912,R091
                     attributes = {
                         **rag_doc.metadata,  # type: ignore[union-attr]
                         "document_id": doc_uuid,
+                        "source": index,
                     }
                     vs_file = await client.vector_stores.files.create(
                         vector_store_id=vector_store.id,
diff --git a/tests/test_document_processor_llama_stack.py b/tests/test_document_processor_llama_stack.py
index 84aefa6..b2b234b 100644
--- a/tests/test_document_processor_llama_stack.py
+++ b/tests/test_document_processor_llama_stack.py
@@ -557,6 +557,12 @@ def test_save_manual_chunking(self, mocker, llama_stack_processor):
         assert call_kwargs["vector_store_id"] == "vs_123"
         assert "chunks" in call_kwargs
         assert len(call_kwargs["chunks"]) == 2
+        # Verify index name is embedded in chunk metadata as "source"
+        # and existing metadata keys are preserved
+        for chunk in call_kwargs["chunks"]:
+            assert chunk["metadata"]["source"] == mock.sentinel.index
+            assert "title" in chunk["metadata"]
+            assert "docs_url" in chunk["metadata"]
 
     def test_save_auto_chunking(self, mocker, llama_stack_processor):
         """Test saving documents with automatic chunking workflow."""
@@ -566,3 +572,9 @@ def test_save_auto_chunking(self, mocker, llama_stack_processor):
         # Verify files.create was called for each document (single file upload)
         assert client.files.create.await_count == 2
         assert client.vector_stores.files.create.await_count == 2
+        # Verify index name is embedded in file attributes as "source"
+        # and existing metadata keys are preserved
+        for call in client.vector_stores.files.create.await_args_list:
+            assert call.kwargs["attributes"]["source"] == mock.sentinel.index
+            assert "title" in call.kwargs["attributes"]
+            assert "document_id" in call.kwargs["attributes"]