diff --git a/samples/langchain_on_vertexai/prebuilt_langchain_agent_template.py b/samples/langchain_on_vertexai/prebuilt_langchain_agent_template.py
index efd7fb58..5202c5a6 100644
--- a/samples/langchain_on_vertexai/prebuilt_langchain_agent_template.py
+++ b/samples/langchain_on_vertexai/prebuilt_langchain_agent_template.py
@@ -75,7 +75,7 @@ def similarity_search(query: str) -> list[Document]:
 # Uncomment to test locally
 
 # app = reasoning_engines.LangchainAgent(
-#     model="gemini-2.0-flash-001",
+#     model="gemini-2.5-flash",
 #     tools=[similarity_search],
 #     model_kwargs={
 #         "temperature": 0.1,
@@ -92,7 +92,7 @@ def similarity_search(query: str) -> list[Document]:
 
 remote_app = reasoning_engines.ReasoningEngine.create(
     reasoning_engines.LangchainAgent(  # type: ignore[arg-type]
-        model="gemini-2.0-flash-001",
+        model="gemini-2.5-flash",
         tools=[similarity_search],  # type: ignore[list-item]
         model_kwargs={
             "temperature": 0.1,
diff --git a/samples/langchain_on_vertexai/requirements.txt b/samples/langchain_on_vertexai/requirements.txt
index aa80c386..72fefdae 100644
--- a/samples/langchain_on_vertexai/requirements.txt
+++ b/samples/langchain_on_vertexai/requirements.txt
@@ -1,5 +1,6 @@
-google-cloud-aiplatform[reasoningengine,langchain]==1.134.0
+google-cloud-aiplatform[reasoningengine,langchain]==2.1.0
 google-cloud-resource-manager==1.16.0
+langchain-classic==1.0.8
 langchain-community==0.3.31
 langchain-google-cloud-sql-pg==0.15.0
 langchain-google-vertexai==2.1.2
diff --git a/samples/langchain_on_vertexai/retriever_agent_with_history_template.py b/samples/langchain_on_vertexai/retriever_agent_with_history_template.py
index bba06a16..1179af9e 100644
--- a/samples/langchain_on_vertexai/retriever_agent_with_history_template.py
+++ b/samples/langchain_on_vertexai/retriever_agent_with_history_template.py
@@ -26,9 +26,9 @@
     TABLE_NAME,
     USER,
 )
-from langchain import hub
-from langchain.agents import AgentExecutor, create_react_agent
-from langchain.tools.retriever import create_retriever_tool
+from langchain_classic import hub
+from langchain_classic.agents import AgentExecutor, create_react_agent
+from langchain_classic.tools.retriever import create_retriever_tool
 from langchain_core.runnables.history import RunnableWithMessageHistory
 from langchain_google_vertexai import ChatVertexAI, VertexAIEmbeddings
 from vertexai.preview import reasoning_engines  # type: ignore
@@ -151,7 +151,7 @@ def query(self, input: str, session_id: str, **kwargs: Any) -> str:  # type: ign
 
 # Uncomment to test locally
 # app = PostgresAgent(
-#     model="gemini-2.0-flash-001",
+#     model="gemini-2.5-flash",
 #     project=PROJECT_ID,
 #     region=REGION,
 #     instance=INSTANCE,
@@ -173,7 +173,7 @@ def query(self, input: str, session_id: str, **kwargs: Any) -> str:  # type: ign
 
 remote_app = reasoning_engines.ReasoningEngine.create(
     PostgresAgent(
-        model="gemini-2.0-flash-001",
+        model="gemini-2.5-flash",
         project=PROJECT_ID,
         region=REGION,
         instance=INSTANCE,
diff --git a/samples/langchain_on_vertexai/retriever_chain_template.py b/samples/langchain_on_vertexai/retriever_chain_template.py
index 0d322ba8..8f03c3d6 100644
--- a/samples/langchain_on_vertexai/retriever_chain_template.py
+++ b/samples/langchain_on_vertexai/retriever_chain_template.py
@@ -25,8 +25,8 @@
     TABLE_NAME,
     USER,
 )
-from langchain.chains.combine_documents import create_stuff_documents_chain
-from langchain.chains.retrieval import create_retrieval_chain
+from langchain_classic.chains.combine_documents import create_stuff_documents_chain
+from langchain_classic.chains.retrieval import create_retrieval_chain
 from langchain_core.prompts import ChatPromptTemplate
 from langchain_google_vertexai import VertexAI, VertexAIEmbeddings
 from vertexai.preview import reasoning_engines  # type: ignore
@@ -123,7 +123,7 @@ def query(self, input: str, **kwargs: Any) -> str:  # type: ignore[override]
 # Uncomment to test locally
 
 # app = PostgresRetriever(
-#     model="gemini-2.0-flash-001",
+#     model="gemini-2.5-flash",
 #     project=PROJECT_ID,
 #     region=REGION,
 #     instance=INSTANCE,
@@ -143,7 +143,7 @@ def query(self, input: str, **kwargs: Any) -> str:  # type: ignore[override]
 
 remote_app = reasoning_engines.ReasoningEngine.create(
     PostgresRetriever(
-        model="gemini-2.0-flash-001",
+        model="gemini-2.5-flash",
         project=PROJECT_ID,
         region=REGION,
         instance=INSTANCE,
diff --git a/samples/requirements.txt b/samples/requirements.txt
index 0cded642..40545224 100644
--- a/samples/requirements.txt
+++ b/samples/requirements.txt
@@ -1,5 +1,6 @@
-google-cloud-aiplatform[reasoningengine,langchain]==1.134.0
+google-cloud-aiplatform[reasoningengine,langchain]==2.1.0
 google-cloud-resource-manager==1.16.0
+langchain-classic==1.0.8
 langchain-community==0.3.29
 langchain-google-cloud-sql-pg==0.15.0
 langchain-google-vertexai==2.1.2