diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index 4c7b94dda2ac..aa8275e5e9ab 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -4901,6 +4901,20 @@ def test_setup_status_reports_provider_config(monkeypatch):
     assert resp["result"]["provider_configured"] is False
 
 
+def test_probe_credentials_emits_exact_empty_key_warning():
+    agent = types.SimpleNamespace(api_key="", provider="openrouter")
+
+    assert server._probe_credentials(agent) == (
+        "No API key configured for provider 'openrouter'. First message will fail."
+    )
+
+
+def test_probe_credentials_allows_keyless_custom_runtime():
+    agent = types.SimpleNamespace(api_key="no-key-required", provider="custom")
+
+    assert server._probe_credentials(agent) == ""
+
+
 def test_setup_runtime_check_rejects_empty_runtime_key(monkeypatch):
     monkeypatch.setattr("hermes_cli.main._has_any_provider_configured", lambda: True)
     monkeypatch.setattr(
@@ -4914,8 +4928,13 @@ def test_setup_runtime_check_rejects_empty_runtime_key(monkeypatch):
 
     resp = server.handle_request({"id": "1", "method": "setup.runtime_check", "params": {}})
 
-    assert resp["result"]["ok"] is False
-    assert resp["result"]["provider"] == "openrouter"
+    assert resp["result"] == {
+        "ok": False,
+        "provider": "openrouter",
+        "model": None,
+        "source": "env/config",
+        "error": "No usable credentials found for openrouter.",
+    }
 
 
 def test_setup_runtime_check_allows_no_key_custom_runtime(monkeypatch):
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 096fb8b546ed..6cc0c8c22d74 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -3866,11 +3866,15 @@ def _get_usage(agent) -> dict:
 
 
 def _probe_credentials(agent) -> str:
-    """Light credential check at session creation — returns warning or ''."""
+    """Light credential check at session creation — returns warning or ''.
+
+    ``no-key-required`` is a valid sentinel for keyless custom providers; only
+    warn when the key is genuinely missing.
+    """
     try:
         key = getattr(agent, "api_key", "") or ""
         provider = getattr(agent, "provider", "") or ""
-        if not key or key == "no-key-required":
+        if not key:
             return f"No API key configured for provider '{provider}'. First message will fail."
     except Exception:
         pass