diff --git a/helpers/settings.py b/helpers/settings.py
index 9eabff9ee..ddeb02d35 100644
--- a/helpers/settings.py
+++ b/helpers/settings.py
@@ -434,6 +434,9 @@ def normalize_settings(settings: Settings) -> Settings:
             except (ValueError, TypeError):
                 copy[key] = value  # make default instead
 
+    if copy["agent_profile"] == "default":
+        copy["agent_profile"] = "agent0"
+
     # mcp server token is set automatically
     copy["mcp_server_token"] = create_auth_token()
     copy["max_consecutive_unusable_responses"] = max(
diff --git a/helpers/settings.py.dox.md b/helpers/settings.py.dox.md
index aaf5b3812..bb6d8656b 100644
--- a/helpers/settings.py.dox.md
+++ b/helpers/settings.py.dox.md
@@ -71,6 +71,8 @@
   A currently configured unavailable profile remains visible with an explicit
   unavailable label so settings can round-trip it truthfully, except that the
   exact `default` utility profile is never offered as a selectable option.
+- Legacy settings that still name the hidden `default` utility profile normalize
+  to `agent0`, so newly created chats always start with a selectable profile.
 - Keep request/response, tool, or helper semantics documented here at the same time as source changes.
 
 ## Work Guidance
diff --git a/tests/test_subagent_profiles.py b/tests/test_subagent_profiles.py
index 605e83fd3..30bf312e6 100644
--- a/tests/test_subagent_profiles.py
+++ b/tests/test_subagent_profiles.py
@@ -5,7 +5,7 @@ from types import SimpleNamespace
 import pytest
 
 from agent import Agent, AgentConfig, AgentContext
-from helpers import persist_chat, projects
+from helpers import persist_chat, projects, settings
 from helpers.errors import RepairableException
 
 
@@ -34,6 +34,13 @@ class _FakeParentAgent:
         return ""
 
 
+def test_hidden_default_profile_normalizes_to_agent0() -> None:
+    configured = settings.get_default_settings()
+    configured["agent_profile"] = "default"
+
+    assert settings.normalize_settings(configured)["agent_profile"] == "agent0"
+
+
 class _FakeSubAgent:
     DATA_NAME_SUPERIOR = "_superior"
     DATA_NAME_SUBORDINATE = "_subordinate"