diff --git a/vertexai/agent_engines/templates/adk.py b/vertexai/agent_engines/templates/adk.py
index f3c186e903..97be3505c6 100644
--- a/vertexai/agent_engines/templates/adk.py
+++ b/vertexai/agent_engines/templates/adk.py
@@ -585,6 +585,7 @@ async def _init_session(
     ):
         """Initializes the session, and returns the session id."""
         from google.adk.events.event import Event
+        import random
 
         session_state = None
         if request.authorizations:
@@ -593,9 +594,14 @@ async def _init_session(
                 auth = _Authorization(**auth)
                 session_state[f"temp:{auth_id}"] = auth.access_token
 
+        if request.session_id:
+            session_id = request.session_id
+        else:
+            session_id = f"temp_session_{random.randbytes(8).hex()}"
         session = await session_service.create_session(
             app_name=self._tmpl_attrs.get("app_name"),
             user_id=request.user_id,
+            session_id=session_id,
             state=session_state,
         )
         if not session:
@@ -613,7 +619,7 @@ async def _init_session(
                     saved_version = await artifact_service.save_artifact(
                         app_name=self._tmpl_attrs.get("app_name"),
                         user_id=request.user_id,
-                        session_id=session.id,
+                        session_id=session_id,
                         filename=artifact.file_name,
                         artifact=version_data.data,
                     )
@@ -1052,53 +1058,35 @@ async def streaming_agent_run_with_events(self, request_json: str):
 
         import json
         from google.genai import types
-        from google.genai.errors import ClientError
 
         request = _StreamRunRequest(**json.loads(request_json))
         if not self._tmpl_attrs.get("in_memory_runner"):
             self.set_up()
-        if not self._tmpl_attrs.get("runner"):
-            self.set_up()
         # Prepare the in-memory session.
         if not self._tmpl_attrs.get("in_memory_artifact_service"):
             self.set_up()
-        if not self._tmpl_attrs.get("artifact_service"):
-            self.set_up()
         if not self._tmpl_attrs.get("in_memory_session_service"):
             self.set_up()
-        if not self._tmpl_attrs.get("session_service"):
-            self.set_up()
+        session_service = self._tmpl_attrs.get("in_memory_session_service")
+        artifact_service = self._tmpl_attrs.get("in_memory_artifact_service")
         app = self._tmpl_attrs.get("app")
-
         # Try to get the session, if it doesn't exist, create a new one.
+        session = None
         if request.session_id:
-            session_service = self._tmpl_attrs.get("session_service")
-            artifact_service = self._tmpl_attrs.get("artifact_service")
-            runner = self._tmpl_attrs.get("runner")
             try:
                 session = await session_service.get_session(
                     app_name=app.name if app else self._tmpl_attrs.get("app_name"),
                     user_id=request.user_id,
                     session_id=request.session_id,
                 )
-            except ClientError:
-                #  Fall back to create session if the session is not found.
-                #  Specifying session_id on creation is not supported,
-                #  so session id will be regenerated.
-                session = await self._init_session(
-                    session_service=session_service,
-                    artifact_service=artifact_service,
-                    request=request,
-                )
-        else:
-            # Not providing a session ID will create a new in-memory session.
-            session_service = self._tmpl_attrs.get("in_memory_session_service")
-            artifact_service = self._tmpl_attrs.get("in_memory_artifact_service")
-            runner = self._tmpl_attrs.get("in_memory_runner")
-            session = await session_service.create_session(
-                app_name=self._tmpl_attrs.get("app_name"),
-                user_id=request.user_id,
-                session_id=request.session_id,
+            except RuntimeError:
+                pass
+        if not session:
+            #  Fall back to create session if the session is not found.
+            session = await self._init_session(
+                session_service=session_service,
+                artifact_service=artifact_service,
+                request=request,
             )
         if not session:
             raise RuntimeError("Session initialization failed.")
@@ -1106,7 +1094,7 @@ async def streaming_agent_run_with_events(self, request_json: str):
         # Run the agent
         message_for_agent = types.Content(**request.message)
         try:
-            async for event in runner.run_async(
+            async for event in self._tmpl_attrs.get("in_memory_runner").run_async(
                 user_id=request.user_id,
                 session_id=session.id,
                 new_message=message_for_agent,
diff --git a/vertexai/preview/reasoning_engines/templates/adk.py b/vertexai/preview/reasoning_engines/templates/adk.py
index 8b49b992c6..1bf5bb64a0 100644
--- a/vertexai/preview/reasoning_engines/templates/adk.py
+++ b/vertexai/preview/reasoning_engines/templates/adk.py
@@ -533,6 +533,7 @@ async def _init_session(
     ):
         """Initializes the session, and returns the session id."""
         from google.adk.events.event import Event
+        import random
 
         session_state = None
         if request.authorizations:
@@ -541,9 +542,14 @@ async def _init_session(
                 auth = _Authorization(**auth)
                 session_state[f"temp:{auth_id}"] = auth.access_token
 
+        if request.session_id:
+            session_id = request.session_id
+        else:
+            session_id = f"temp_session_{random.randbytes(8).hex()}"
         session = await session_service.create_session(
             app_name=self._tmpl_attrs.get("app_name"),
             user_id=request.user_id,
+            session_id=session_id,
             state=session_state,
         )
         if not session:
@@ -561,7 +567,7 @@ async def _init_session(
                     saved_version = await artifact_service.save_artifact(
                         app_name=self._tmpl_attrs.get("app_name"),
                         user_id=request.user_id,
-                        session_id=session.id,
+                        session_id=session_id,
                         filename=artifact.file_name,
                         artifact=version_data.data,
                     )
@@ -939,7 +945,6 @@ async def async_stream_query(
     def streaming_agent_run_with_events(self, request_json: str):
         import json
         from google.genai import types
-        from google.genai.errors import ClientError
 
         event_queue = queue.Queue(maxsize=1)
 
@@ -947,52 +952,37 @@ async def _invoke_agent_async():
             request = _StreamRunRequest(**json.loads(request_json))
             if not self._tmpl_attrs.get("in_memory_runner"):
                 self.set_up()
-            if not self._tmpl_attrs.get("runner"):
-                self.set_up()
             # Prepare the in-memory session.
             if not self._tmpl_attrs.get("in_memory_artifact_service"):
                 self.set_up()
-            if not self._tmpl_attrs.get("artifact_service"):
-                self.set_up()
             if not self._tmpl_attrs.get("in_memory_session_service"):
                 self.set_up()
-            if not self._tmpl_attrs.get("session_service"):
-                self.set_up()
+            session_service = self._tmpl_attrs.get("in_memory_session_service")
+            artifact_service = self._tmpl_attrs.get("in_memory_artifact_service")
+            # Try to get the session, if it doesn't exist, create a new one.
+            session = None
             if request.session_id:
-                session_service = self._tmpl_attrs.get("session_service")
-                artifact_service = self._tmpl_attrs.get("artifact_service")
-                runner = self._tmpl_attrs.get("runner")
                 try:
                     session = await session_service.get_session(
                         app_name=self._tmpl_attrs.get("app_name"),
                         user_id=request.user_id,
                         session_id=request.session_id,
                     )
-                except ClientError:
-                    #  Fall back to create session if the session is not found.
-                    #  Specifying session_id on creation is not supported,
-                    #  so session id will be regenerated.
-                    session = await self._init_session(
-                        session_service=session_service,
-                        artifact_service=artifact_service,
-                        request=request,
-                    )
-            else:
-                # Not providing a session ID will create a new in-memory session.
-                session_service = self._tmpl_attrs.get("in_memory_session_service")
-                artifact_service = self._tmpl_attrs.get("in_memory_artifact_service")
-                runner = self._tmpl_attrs.get("in_memory_runner")
-                session = await session_service.create_session(
-                    app_name=self._tmpl_attrs.get("app_name"),
-                    user_id=request.user_id,
-                    session_id=request.session_id,
+                except RuntimeError:
+                    pass
+            if not session:
+                #  Fall back to create session if the session is not found.
+                session = await self._init_session(
+                    session_service=session_service,
+                    artifact_service=artifact_service,
+                    request=request,
                 )
             if not session:
                 raise RuntimeError("Session initialization failed.")
             # Run the agent.
             message_for_agent = types.Content(**request.message)
             try:
-                for event in runner.run(
+                for event in self._tmpl_attrs.get("in_memory_runner").run(
                     user_id=request.user_id,
                     session_id=session.id,
                     new_message=message_for_agent,