diff --git a/src/google/adk/memory/in_memory_memory_service.py b/src/google/adk/memory/in_memory_memory_service.py
index 124915314d..e85496f757 100644
--- a/src/google/adk/memory/in_memory_memory_service.py
+++ b/src/google/adk/memory/in_memory_memory_service.py
@@ -15,6 +15,7 @@
 
 from collections.abc import Mapping
 from collections.abc import Sequence
+from copy import deepcopy
 import itertools
 import re
 import threading
@@ -98,7 +99,7 @@ async def add_session_to_memory(self, session: Session) -> None:
     with self._lock:
       self._session_events[user_key] = self._session_events.get(user_key, {})
       self._session_events[user_key][session.id] = [
-          event
+          event.model_copy(update={'content': deepcopy(event.content)})
           for event in session.events
           if event.content and event.content.parts
       ]
@@ -128,7 +129,10 @@ async def add_events_to_memory(
       existing_ids = {event.id for event in existing_events}
       for event in events_to_add:
         if event.id not in existing_ids:
-          existing_events.append(event)
+          # Snapshot the fields used by memory without copying opaque outputs.
+          existing_events.append(
+              event.model_copy(update={'content': deepcopy(event.content)})
+          )
           existing_ids.add(event.id)
       self._session_events[user_key][scoped_session_id] = existing_events
 
@@ -186,5 +190,8 @@ async def search_memory(
     # so it is stable and events matching equally stay in insertion order.
     scored_memories.sort(key=lambda scored_memory: -scored_memory[0])
     return SearchMemoryResponse(
-        memories=[memory for _, memory in scored_memories[:_MAX_SEARCH_RESULTS]]
+        memories=[
+            memory.model_copy(update={'content': deepcopy(memory.content)})
+            for _, memory in scored_memories[:_MAX_SEARCH_RESULTS]
+        ]
     )
diff --git a/tests/unittests/memory/test_in_memory_memory_service.py b/tests/unittests/memory/test_in_memory_memory_service.py
index 1e95bfceb1..93dea40e34 100644
--- a/tests/unittests/memory/test_in_memory_memory_service.py
+++ b/tests/unittests/memory/test_in_memory_memory_service.py
@@ -602,3 +602,88 @@ def reader():
   assert (
       not errors
   ), f'search_memory raced with concurrent writes: {errors[0]!r}'
+
+
+@pytest.mark.parametrize('ingest_session', [True, False])
+async def test_ingested_memories_do_not_follow_caller_event_mutations(
+    ingest_session: bool,
+) -> None:
+  """Changing an ingested event does not rewrite the stored memory."""
+  service = InMemoryMemoryService()
+  event = Event(
+      id='event',
+      author='user',
+      timestamp=12345,
+      content=types.Content(parts=[types.Part(text='I prefer jasmine tea.')]),
+  )
+  session = Session(
+      app_name=MOCK_APP_NAME,
+      user_id=MOCK_USER_ID,
+      id='session',
+      events=[event],
+  )
+  if ingest_session:
+    await service.add_session_to_memory(session)
+  else:
+    await service.add_events_to_memory(
+        app_name=session.app_name,
+        user_id=session.user_id,
+        session_id=session.id,
+        events=session.events,
+    )
+
+  event.author = 'changed'
+  event.content.parts[0].text = 'I prefer coffee.'
+  result = await service.search_memory(
+      app_name=MOCK_APP_NAME, user_id=MOCK_USER_ID, query='jasmine'
+  )
+
+  assert len(result.memories) == 1
+  assert result.memories[0].author == 'user'
+  assert result.memories[0].content.parts[0].text == 'I prefer jasmine tea.'
+
+
+@pytest.mark.parametrize('ingest_session', [True, False])
+async def test_retrieved_memories_do_not_mutate_storage_or_session_history(
+    ingest_session: bool,
+) -> None:
+  """Editing a search result leaves subsequent recall and its source intact."""
+  service = InMemoryMemoryService()
+  session = Session(
+      app_name=MOCK_APP_NAME,
+      user_id=MOCK_USER_ID,
+      id='session',
+      events=[
+          Event(
+              id='event',
+              author='user',
+              timestamp=12345,
+              content=types.Content(
+                  parts=[types.Part(text='I prefer jasmine tea.')]
+              ),
+          ),
+      ],
+  )
+  if ingest_session:
+    await service.add_session_to_memory(session)
+  else:
+    await service.add_events_to_memory(
+        app_name=session.app_name,
+        user_id=session.user_id,
+        session_id=session.id,
+        events=session.events,
+    )
+  first_result = await service.search_memory(
+      app_name=MOCK_APP_NAME, user_id=MOCK_USER_ID, query='jasmine'
+  )
+
+  first_result.memories[0].content.parts.clear()
+  second_result = await service.search_memory(
+      app_name=MOCK_APP_NAME, user_id=MOCK_USER_ID, query='jasmine'
+  )
+
+  assert len(second_result.memories) == 1
+  assert (
+      second_result.memories[0].content.parts[0].text == 'I prefer jasmine tea.'
+  )
+  assert session.events[0].content.parts[0].text == 'I prefer jasmine tea.'