diff --git a/agents/rag/setup_corpus.py b/agents/rag/setup_corpus.py
index c2bc549..7998f32 100644
--- a/agents/rag/setup_corpus.py
+++ b/agents/rag/setup_corpus.py
@@ -3,8 +3,12 @@
 setup_corpus.py — Create a Vertex AI RAG Engine corpus and import documents.
 Project: propane-will-491900-m5
 
-Explicitly uses Serverless (RagManagedDbConfig basic tier) to avoid
+Explicitly uses Serverless (RagManagedDb basic tier) to avoid
 Spanner allowlist restrictions on new projects in us-central1.
+
+Tested against vertexai SDK 1.153.1:
+  RagVectorDbConfig(vector_db=RagManagedDb(tier=1))
+  tier=1 == BASIC (serverless), tier=2 == ENTERPRISE
 """
 
 import os
@@ -23,8 +27,7 @@ GCS_SOURCE = os.environ.get(
     f"gs://{PROJECT_ID}-agent-staging/rag-docs/",
 )
 
-# RagManagedDbConfig.Tier enum may not exist in older SDK versions.
-# tier=1 == BASIC, tier=2 == ENTERPRISE
+# tier=1 == BASIC (serverless), tier=2 == ENTERPRISE
 _TIER_BASIC = 1
 
 
@@ -81,8 +84,8 @@ def get_or_create_corpus() -> RagCorpus:
     corpus = rag.create_corpus(
         display_name=CORPUS_DISPLAY_NAME,
         backend_config=rag.RagVectorDbConfig(
-            rag_managed_db=rag.RagManagedDbConfig(
-                tier=_TIER_BASIC,  # 1 = BASIC (serverless), 2 = ENTERPRISE
+            vector_db=rag.RagManagedDb(
+                tier=_TIER_BASIC,  # 1 = BASIC (serverless)
             )
         ),
     )