diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 8cb68f2a0ad2..9bf623ea0884 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -339,6 +339,12 @@ def _is_arcee_trinity_thinking(model: Optional[str]) -> bool:
     return bare == "trinity-large-thinking"
 
 
+def _is_gpt55_family(model: Optional[str]) -> bool:
+    """Return whether *model* belongs to the gpt-5.5 family."""
+    bare = (model or "").strip().lower().rsplit("/", 1)[-1]
+    return bare == "gpt-5.5" or bare.startswith(("gpt-5.5-", "gpt-5.5."))
+
+
 # Context window enforced by ChatGPT's Codex OAuth backend for the
 # gpt-5.4 / gpt-5.5 / gpt-5.6 families. The raw OpenAI API and OpenRouter
 # expose 1.05M for the same slugs, but the Codex backend hard-caps at 272K
@@ -426,6 +432,9 @@ def _fixed_temperature_for_model(
         return OMIT_TEMPERATURE
     if _is_arcee_trinity_thinking(model):
         return 0.5
+    if _is_gpt55_family(model):
+        logger.debug("Omitting temperature for gpt-5.5 family model %r (default-only)", model)
+        return OMIT_TEMPERATURE
     return None
 
 
diff --git a/tests/agent/test_unsupported_temperature_retry.py b/tests/agent/test_unsupported_temperature_retry.py
index fd9c72ef97f0..1eea09b9df0a 100644
--- a/tests/agent/test_unsupported_temperature_retry.py
+++ b/tests/agent/test_unsupported_temperature_retry.py
@@ -28,6 +28,10 @@
 import pytest
 
 from agent.auxiliary_client import (
+    OMIT_TEMPERATURE,
+    _build_call_kwargs,
+    _fixed_temperature_for_model,
+    _is_gpt55_family,
     call_llm,
     async_call_llm,
     _is_unsupported_temperature_error,
@@ -74,6 +78,42 @@ def _dummy_response():
     return {"ok": True}
 
 
+@pytest.mark.parametrize(
+    "model",
+    [
+        "gpt-5.5",
+        "gpt-5.5-pro",
+        "gpt-5.5-2026-04-23",
+        "openai/gpt-5.5",
+        "GPT-5.5",
+        "  gpt-5.5  ",
+    ],
+)
+def test_gpt55_family_omits_temperature(model):
+    assert _is_gpt55_family(model) is True
+    assert _fixed_temperature_for_model(model) is OMIT_TEMPERATURE
+
+
+@pytest.mark.parametrize(
+    "model",
+    [None, "", "gpt-5.4", "gpt-5.55", "gpt-5.50", "gpt-55", "gpt-4o"],
+)
+def test_gpt55_family_rejects_near_misses(model):
+    assert _is_gpt55_family(model) is False
+
+
+def test_gpt55_call_kwargs_omit_temperature():
+    kwargs = _build_call_kwargs(
+        provider="openai-api",
+        model="gpt-5.5-pro",
+        messages=[{"role": "user", "content": "hi"}],
+        temperature=0.1,
+        timeout=120.0,
+    )
+    assert "temperature" not in kwargs
+    assert kwargs["model"] == "gpt-5.5-pro"
+
+
 class TestCallLlmUnsupportedTemperatureRetry:
     """``call_llm`` retries once without temperature and returns on success."""
 
@@ -93,9 +133,9 @@ def test_retries_once_without_temperature(self, error_message):
 
         with (
             patch("agent.auxiliary_client._resolve_task_provider_model",
-                  return_value=("openai-codex", "gpt-5.5", None, None, None)),
+                  return_value=("openai-codex", "gpt-5.4", None, None, None)),
             patch("agent.auxiliary_client._get_cached_client",
-                  return_value=(client, "gpt-5.5")),
+                  return_value=(client, "gpt-5.4")),
             patch("agent.auxiliary_client._validate_llm_response",
                   side_effect=lambda resp, _task, **_kw: resp),
         ):
@@ -120,6 +160,30 @@ def test_retries_once_without_temperature(self, error_message):
         assert "max_tokens" not in retry_kwargs
         assert retry_kwargs["model"] == first_kwargs["model"]
 
+    def test_gpt55_family_succeeds_without_reactive_retry(self):
+        client = MagicMock()
+        client.base_url = "https://api.openai.com/v1"
+        client.chat.completions.create.return_value = _dummy_response()
+
+        with (
+            patch("agent.auxiliary_client._resolve_task_provider_model",
+                  return_value=("openai-codex", "gpt-5.5", None, None, None)),
+            patch("agent.auxiliary_client._get_cached_client",
+                  return_value=(client, "gpt-5.5")),
+            patch("agent.auxiliary_client._validate_llm_response",
+                  side_effect=lambda resp, _task, **_kw: resp),
+        ):
+            result = call_llm(
+                task="compression",
+                messages=[{"role": "user", "content": "remember this"}],
+                temperature=0.3,
+                max_tokens=500,
+            )
+
+        assert result == {"ok": True}
+        assert client.chat.completions.create.call_count == 1
+        assert "temperature" not in client.chat.completions.create.call_args.kwargs
+
     def test_non_temperature_400_does_not_retry_as_temperature(self):
         """Unrelated 400s (e.g. bad tool role) must not silently drop temp."""
         client = MagicMock()
@@ -193,9 +257,9 @@ async def test_async_retries_once_without_temperature(self):
 
         with (
             patch("agent.auxiliary_client._resolve_task_provider_model",
-                  return_value=("openai-codex", "gpt-5.5", None, None, None)),
+                  return_value=("openai-codex", "gpt-5.4", None, None, None)),
             patch("agent.auxiliary_client._get_cached_client",
-                  return_value=(client, "gpt-5.5")),
+                  return_value=(client, "gpt-5.4")),
             patch("agent.auxiliary_client._validate_llm_response",
                   side_effect=lambda resp, _task, **_kw: resp),
         ):