diff --git a/tests/integration/test_api_contract.py b/tests/integration/test_api_contract.py
new file mode 100644
index 0000000..edaa52a
--- /dev/null
+++ b/tests/integration/test_api_contract.py
@@ -0,0 +1,23 @@
+from fastapi.testclient import TestClient
+
+from supportagent.api import app
+
+client = TestClient(app)
+
+
+def test_models_endpoint_returns_model_catalog_and_request_id():
+    response = client.get("/models")
+
+    assert response.status_code == 200
+    assert "models" in response.json()
+    assert response.headers["X-Request-ID"]
+
+
+def test_ask_requires_authentication():
+    response = client.post(
+        "/ask",
+        json={"question": "Wie funktioniert das?"},
+    )
+
+    assert response.status_code == 401
+    assert response.headers["X-Request-ID"]