diff --git a/src/google/adk/sessions/vertex_ai_session_service.py b/src/google/adk/sessions/vertex_ai_session_service.py
index 6628eb95..eac13367 100644
--- a/src/google/adk/sessions/vertex_ai_session_service.py
+++ b/src/google/adk/sessions/vertex_ai_session_service.py
@@ -25,6 +25,11 @@ import urllib.parse
 
 from dateutil import parser
 from google.genai.errors import ClientError
+from tenacity import retry
+from tenacity import retry_if_result
+from tenacity import RetryError
+from tenacity import stop_after_attempt
+from tenacity import wait_exponential
 from typing_extensions import override
 
 from google import genai
@@ -64,6 +69,20 @@ class VertexAiSessionService(BaseSessionService):
     self._location = location
     self._agent_engine_id = agent_engine_id
 
+  async def _get_session_api_response(
+      self,
+      reasoning_engine_id: str,
+      session_id: str,
+      api_client: genai.ApiClient,
+  ):
+    get_session_api_response = await api_client.async_request(
+        http_method='GET',
+        path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}',
+        request_dict={},
+    )
+    get_session_api_response = _convert_api_response(get_session_api_response)
+    return get_session_api_response
+
   @override
   async def create_session(
       self,
@@ -95,66 +114,68 @@ class VertexAiSessionService(BaseSessionService):
 
     session_id = api_response['name'].split('/')[-3]
     operation_id = api_response['name'].split('/')[-1]
-
-    max_retry_attempt = 5
-
     if _is_vertex_express_mode(self._project, self._location):
       # Express mode doesn't support LRO, so we need to poll
       # the session resource.
       # TODO: remove this once LRO polling is supported in Express mode.
-      for i in range(max_retry_attempt):
+      @retry(
+          stop=stop_after_attempt(5),
+          wait=wait_exponential(multiplier=1, min=1, max=3),
+          retry=retry_if_result(lambda response: not response),
+          reraise=True,
+      )
+      async def _poll_session_resource():
         try:
-          await api_client.async_request(
-              http_method='GET',
-              path=(
-                  f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}'
-              ),
-              request_dict={},
+          return await self._get_session_api_response(
+              reasoning_engine_id, session_id, api_client
           )
-          break
-        except ClientError as e:
-          logger.info('Polling for session %s: %s', session_id, e)
-          # Add slight exponential backoff to avoid excessive polling.
-          await asyncio.sleep(1 + 0.5 * i)
-      else:
-        raise TimeoutError('Session creation failed.')
+        except ClientError:
+          logger.info(f'Polling session resource')
+          return None
+
+      try:
+        await _poll_session_resource()
+      except Exception as exc:
+        raise ValueError('Failed to create session.') from exc
     else:
-      lro_response = None
-      for _ in range(max_retry_attempt):
+
+      @retry(
+          stop=stop_after_attempt(5),
+          wait=wait_exponential(multiplier=1, min=1, max=3),
+          retry=retry_if_result(
+              lambda response: not response.get('done', False),
+          ),
+          reraise=True,
+      )
+      async def _poll_lro():
         lro_response = await api_client.async_request(
             http_method='GET',
             path=f'operations/{operation_id}',
             request_dict={},
         )
         lro_response = _convert_api_response(lro_response)
+        return lro_response
 
-        if lro_response.get('done', None):
-          break
-
-        await asyncio.sleep(1)
-
-      if lro_response is None or not lro_response.get('done', None):
+      try:
+        await _poll_lro()
+      except RetryError as exc:
         raise TimeoutError(
             f'Timeout waiting for operation {operation_id} to complete.'
-        )
+        ) from exc
+      except Exception as exc:
+        raise ValueError('Failed to create session.') from exc
 
-    # Get session resource
-    get_session_api_response = await api_client.async_request(
-        http_method='GET',
-        path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}',
-        request_dict={},
+    get_session_api_response = await self._get_session_api_response(
+        reasoning_engine_id, session_id, api_client
     )
-    get_session_api_response = _convert_api_response(get_session_api_response)
-
-    update_timestamp = isoparse(
-        get_session_api_response['updateTime']
-    ).timestamp()
     session = Session(
         app_name=str(app_name),
         user_id=str(user_id),
         id=str(session_id),
         state=get_session_api_response.get('sessionState', {}),
-        last_update_time=update_timestamp,
+        last_update_time=isoparse(
+            get_session_api_response['updateTime']
+        ).timestamp(),
     )
     return session
 
@@ -171,12 +192,9 @@ class VertexAiSessionService(BaseSessionService):
     api_client = self._get_api_client()
 
     # Get session resource
-    get_session_api_response = await api_client.async_request(
-        http_method='GET',
-        path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}',
-        request_dict={},
+    get_session_api_response = await self._get_session_api_response(
+        reasoning_engine_id, session_id, api_client
     )
-    get_session_api_response = _convert_api_response(get_session_api_response)
 
     if get_session_api_response['userId'] != user_id:
       raise ValueError(f'Session not found: {session_id}')