diff --git a/src/google/adk/sessions/vertex_ai_session_service.py b/src/google/adk/sessions/vertex_ai_session_service.py
index a465044dd2..5bb310a09e 100644
--- a/src/google/adk/sessions/vertex_ai_session_service.py
+++ b/src/google/adk/sessions/vertex_ai_session_service.py
@@ -556,10 +556,13 @@ def _from_api_event(api_event_obj: vertexai.types.SessionEvent) -> Event:
     event_dict = copy.deepcopy(raw_event_dict)
     timestamp_obj = getattr(api_event_obj, 'timestamp', None)
     event_dict.update({
-        'id': api_event_obj.name.split('/')[-1],
         'invocation_id': getattr(api_event_obj, 'invocation_id', None),
         'author': getattr(api_event_obj, 'author', None),
     })
+    # Preserve the original ADK event id from raw_event so it stays stable
+    # across streaming and reload; only fall back to the Vertex resource
+    # name if raw_event lacks an id (older data).
+    event_dict.setdefault('id', api_event_obj.name.split('/')[-1])
     if timestamp_obj:
       event_dict['timestamp'] = timestamp_obj.timestamp()
     return Event.model_validate(event_dict)
diff --git a/tests/unittests/sessions/test_vertex_ai_session_service.py b/tests/unittests/sessions/test_vertex_ai_session_service.py
index b589d8c368..d286fb8a9a 100644
--- a/tests/unittests/sessions/test_vertex_ai_session_service.py
+++ b/tests/unittests/sessions/test_vertex_ai_session_service.py
@@ -248,6 +248,24 @@ def _generate_mock_events_for_session_5(num_events):
     },
 }]
 
+MOCK_EVENT_WITH_RAW_EVENT_ID_JSON = [{
+    'name': (
+        'projects/test-project/locations/test-location/'
+        'reasoningEngines/123/sessions/override/events/658731057016733696'
+    ),
+    'invocationId': 'e-1',
+    'author': 'user_with_override',
+    'timestamp': '2024-12-12T12:12:12.123456Z',
+    'content': {},
+    'actions': {},
+    'rawEvent': {
+        'id': 'c452feb0-b9ad-48b1-b863-c7dd2f085378',
+        'invocationId': 'e-1',
+        'author': 'user_with_override',
+        'content': {},
+    },
+}]
+
 MOCK_SESSION_WITH_OVERRIDE_JSON = {
     'name': (
         'projects/test-project/locations/test-location/'
@@ -888,6 +906,33 @@ async def test_get_session_from_raw_event(
   assert event.error_message == 'raw_event_error'
 
 
+@pytest.mark.asyncio
+@pytest.mark.usefixtures('mock_get_api_client')
+async def test_get_session_preserves_original_event_id_from_raw_event(
+    mock_api_client_instance: MockAsyncClient,
+) -> None:
+  """get_session should keep the original ADK Event.id persisted in raw_event.
+
+  Regression test for the raw_event id being overwritten by the Vertex event
+  resource name, which made the same logical event report a different id
+  depending on whether it was observed via streaming or via a reload.
+  """
+  mock_api_client_instance.session_dict['6'] = MOCK_SESSION_WITH_OVERRIDE_JSON
+  mock_api_client_instance.event_dict['6'] = (
+      copy.deepcopy(MOCK_EVENT_WITH_RAW_EVENT_ID_JSON),
+      None,
+  )
+  session_service = mock_vertex_ai_session_service()
+  session = await session_service.get_session(
+      app_name='123', user_id='user_with_override', session_id='6'
+  )
+  assert session is not None
+  assert len(session.events) == 1
+  assert (
+      session.events[0].id == 'c452feb0-b9ad-48b1-b863-c7dd2f085378'
+  ), 'Event.id should come from raw_event, not the Vertex resource name.'
+
+
 @pytest.mark.asyncio
 @pytest.mark.usefixtures('mock_get_api_client')
 async def test_get_session_with_many_events(mock_api_client_instance):