diff --git a/tests/unit/vertex_adk/test_agent_engine_templates_adk.py b/tests/unit/vertex_adk/test_agent_engine_templates_adk.py
index 93b10c1214..f7eb3e1ade 100644
--- a/tests/unit/vertex_adk/test_agent_engine_templates_adk.py
+++ b/tests/unit/vertex_adk/test_agent_engine_templates_adk.py
@@ -63,7 +63,7 @@ def __init__(self, name: str, model: str):
 _TEST_AGENT = Agent(name=_TEST_AGENT_NAME, model=_TEST_MODEL)
 _TEST_SESSION = {
     "id": "ca18c25a-644b-4e13-9b24-78c150ec3eb9",
-    "app_name": "default-app-name",
+    "app_name": "default_app_name",
     "user_id": _TEST_USER_ID,
     "events": [
         {
diff --git a/vertexai/agent_engines/templates/adk.py b/vertexai/agent_engines/templates/adk.py
index 1144e7d096..178160c6aa 100644
--- a/vertexai/agent_engines/templates/adk.py
+++ b/vertexai/agent_engines/templates/adk.py
@@ -93,7 +93,7 @@
         SynchronousMultiSpanProcessor = Any
 
 
-_DEFAULT_APP_NAME = "default-app-name"
+_DEFAULT_APP_NAME = "default_app_name"
 _DEFAULT_USER_ID = "default-user-id"
 _TELEMETRY_API_DISABLED_WARNING = (
     "Tracing integration for Agent Engine has migrated to a new API.\n"