diff --git a/tests/run_agent/test_run_agent.py b/tests/run_agent/test_run_agent.py
index 7aec0e3dde25..c218e75564ee 100644
--- a/tests/run_agent/test_run_agent.py
+++ b/tests/run_agent/test_run_agent.py
@@ -1995,23 +1995,38 @@ class TestBuildApiKwargs:
         )
         assert kwargs["extra_body"]["reasoning"] == {"effort": "medium"}
 
-    def test_reasoning_xhigh_normalized_for_copilot(self, agent):
-        """xhigh effort should normalize to high for Copilot GitHub Models."""
+    def test_reasoning_xhigh_preserved_for_copilot_when_supported(self, agent, monkeypatch):
+        """The registered Copilot profile must preserve a supported xhigh."""
         from agent.transports import get_transport
         from providers import get_provider_profile
 
+        monkeypatch.setattr(
+            "hermes_cli.models.github_model_reasoning_efforts",
+            lambda _model: ["none", "low", "medium", "high", "xhigh"],
+        )
         transport = get_transport("chat_completions")
         profile = get_provider_profile("copilot")
         msgs = [{"role": "user", "content": "hi"}]
         kwargs = transport.build_kwargs(
-            model="gpt-5.4",
+            model="gpt-5.5",
             messages=msgs,
             tools=None,
             supports_reasoning=True,
             reasoning_config={"enabled": True, "effort": "xhigh"},
             provider_profile=profile,
         )
-        assert kwargs["extra_body"]["reasoning"] == {"effort": "high"}
+        assert kwargs["extra_body"]["reasoning"] == {"effort": "xhigh"}
+
+    def test_core_responses_preserves_supported_xhigh(self, agent, monkeypatch):
+        """The core GitHub Responses path must preserve a supported xhigh."""
+        monkeypatch.setattr(
+            "hermes_cli.models.github_model_reasoning_efforts",
+            lambda _model: ["none", "low", "medium", "high", "xhigh"],
+        )
+        agent.model = "gpt-5.5"
+        agent.reasoning_config = {"enabled": True, "effort": "xhigh"}
+
+        assert agent._github_models_reasoning_extra_body() == {"effort": "xhigh"}
 
     def test_reasoning_omitted_for_non_reasoning_copilot_model(self, agent):
         agent.base_url = "https://api.githubcopilot.com"