diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 5cdb590dd5d..ba5f02ba867 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -278,17 +278,31 @@ def interruptible_api_call(agent, api_kwargs: dict):
         _elapsed = time.time() - _call_start
         if _elapsed > _stale_timeout:
             _est_ctx = estimate_request_context_tokens(api_kwargs)
+            _silent_hint: Optional[str] = None
+            _hint_fn = getattr(agent, "_codex_silent_hang_hint", None)
+            if callable(_hint_fn):
+                try:
+                    _silent_hint = _hint_fn(model=api_kwargs.get("model"))
+                except Exception:
+                    _silent_hint = None
             logger.warning(
                 "Non-streaming API call stale for %.0fs (threshold %.0fs). "
                 "model=%s context=~%s tokens. Killing connection.",
                 _elapsed, _stale_timeout,
                 api_kwargs.get("model", "unknown"), f"{_est_ctx:,}",
             )
-            agent._emit_status(
-                f"⚠️ No response from provider for {int(_elapsed)}s "
-                f"(non-streaming, model: {api_kwargs.get('model', 'unknown')}). "
-                f"Aborting call."
-            )
+            if _silent_hint:
+                agent._emit_status(
+                    f"⚠️ No response from provider for {int(_elapsed)}s "
+                    f"(non-streaming, model: {api_kwargs.get('model', 'unknown')}). "
+                    f"{_silent_hint}"
+                )
+            else:
+                agent._emit_status(
+                    f"⚠️ No response from provider for {int(_elapsed)}s "
+                    f"(non-streaming, model: {api_kwargs.get('model', 'unknown')}). "
+                    f"Aborting call."
+                )
             try:
                 if agent.api_mode == "anthropic_messages":
                     agent._anthropic_client.close()
@@ -303,10 +317,17 @@ def interruptible_api_call(agent, api_kwargs: dict):
             # Wait briefly for the thread to notice the closed connection.
             t.join(timeout=2.0)
             if result["error"] is None and result["response"] is None:
-                result["error"] = TimeoutError(
-                    f"Non-streaming API call timed out after {int(_elapsed)}s "
-                    f"with no response (threshold: {int(_stale_timeout)}s)"
-                )
+                if _silent_hint:
+                    result["error"] = TimeoutError(
+                        f"Non-streaming API call timed out after {int(_elapsed)}s "
+                        f"with no response (threshold: {int(_stale_timeout)}s). "
+                        f"{_silent_hint}"
+                    )
+                else:
+                    result["error"] = TimeoutError(
+                        f"Non-streaming API call timed out after {int(_elapsed)}s "
+                        f"with no response (threshold: {int(_stale_timeout)}s)"
+                    )
             break
 
         if agent._interrupt_requested:
diff --git a/run_agent.py b/run_agent.py
index 6c44c2d9a48..d2d65314f75 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -927,6 +927,57 @@ class AIAgent:
             return max(stale_base, 150.0)
         return stale_base
 
+    def _codex_silent_hang_hint(self, model: Optional[str] = None) -> Optional[str]:
+        """Return an actionable hint when this request matches a known
+        Codex silent-reject configuration, else ``None``.
+
+        The ChatGPT Codex backend (``chatgpt.com/backend-api/codex``) has
+        historically silently dropped certain model requests: the connection
+        is accepted but no stream events are emitted and no error is raised.
+        The stale-call detector ends the hang, but a generic "timed out"
+        message gives the user no path forward.
+
+        This helper substitutes an actionable hint into the stale-timeout
+        warning when the request matches a known silent-reject pattern.
+        Currently flagged: ``gpt-5.5`` family on the Codex backend.  See
+        hermes-agent #21444 for the symptom history.  The upstream backend
+        behavior has historically come and gone with ChatGPT entitlement
+        changes — the heuristic stays in place as future-proofing even when
+        the symptom is dormant.
+
+        Does NOT fix the backend issue.  Only converts an opaque stale-timeout
+        into actionable text so users learn the workaround in seconds rather
+        than digging through logs.
+        """
+        if self.api_mode != "codex_responses":
+            return None
+        is_codex_backend = (
+            self.provider == "openai-codex"
+            or (
+                getattr(self, "_base_url_hostname", "") == "chatgpt.com"
+                and "/backend-api/codex" in (getattr(self, "_base_url_lower", "") or "")
+            )
+        )
+        if not is_codex_backend:
+            return None
+        eff_model = (model if model is not None else self.model) or ""
+        model_lower = eff_model.lower()
+        # Match the gpt-5.5 family — bare ``gpt-5.5``, ``gpt-5.5-codex``,
+        # vendor-prefixed variants like ``openai/gpt-5.5``, and any future
+        # ``gpt-5.5-*`` SKU.  Anchor at a word boundary on either side so
+        # unrelated tokens like ``gpt-5.50`` do not match.
+        if not re.search(r"(?:^|[/\-_])gpt-5\.5(?:$|[\-_])", model_lower):
+            return None
+        return (
+            f"Codex backend appears to be silently rejecting {eff_model!r} "
+            "on chatgpt.com/backend-api/codex (no stream events, no error). "
+            "This is a known backend-side pattern that has affected ChatGPT "
+            "Plus accounts intermittently. "
+            "Workaround: try `gpt-5.4-codex` on the same OAuth profile, "
+            "or switch to a different model/provider in your fallback chain. "
+            "See hermes-agent#21444 for symptom history."
+        )
+
     def _is_openrouter_url(self) -> bool:
         """Return True when the base URL targets OpenRouter."""
         return base_url_host_matches(self._base_url_lower, "openrouter.ai")
diff --git a/scripts/release.py b/scripts/release.py
index 2f6f41a7157..be323e148d5 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -595,6 +595,7 @@ AUTHOR_MAP = {
     "mgparkprint@gmail.com": "vlwkaos",
     "1317078257maroon@gmail.com": "Oxidane-bot",
     "tranquil_flow@protonmail.com": "Tranquil-Flow",
+    "66773372+Tranquil-Flow@users.noreply.github.com": "Tranquil-Flow",
     "LyleLengyel@gmail.com": "mcndjxlefnd",
     "wangshengyang2004@163.com": "Wangshengyang2004",
     "hasan.ali13381@gmail.com": "H-Ali13381",
diff --git a/tests/run_agent/test_codex_silent_hang_hint.py b/tests/run_agent/test_codex_silent_hang_hint.py
new file mode 100644
index 00000000000..db10da61aa2
--- /dev/null
+++ b/tests/run_agent/test_codex_silent_hang_hint.py
@@ -0,0 +1,121 @@
+"""Tests for the ``_codex_silent_hang_hint`` heuristic.
+
+The helper substitutes an actionable hint into the stale-call timeout
+warning when the request matches a known Codex silent-reject pattern
+(gpt-5.5 family on the ChatGPT Codex backend).  See issue #21444 for
+symptom history.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+
+def _make_agent(tmp_path: Path, **overrides):
+    from run_agent import AIAgent
+    kwargs = dict(
+        model="gpt-5.5",
+        provider="openai-codex",
+        api_key="sk-dummy",
+        base_url="https://chatgpt.com/backend-api/codex",
+        quiet_mode=True,
+        skip_context_files=True,
+        skip_memory=True,
+        platform="cli",
+    )
+    kwargs.update(overrides)
+    return AIAgent(**kwargs)
+
+
+@pytest.fixture(autouse=True)
+def _isolate_hermes_home(monkeypatch, tmp_path):
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    (tmp_path / ".env").write_text("", encoding="utf-8")
+
+
+# ── positive cases: hint fires ─────────────────────────────────────────────
+
+
+def test_hint_fires_for_bare_gpt_5_5_on_codex(tmp_path):
+    agent = _make_agent(tmp_path)
+    agent.api_mode = "codex_responses"
+    hint = agent._codex_silent_hang_hint(model="gpt-5.5")
+    assert hint is not None
+    assert "gpt-5.4-codex" in hint
+    assert "fallback chain" in hint
+
+
+def test_hint_fires_for_vendor_prefixed_gpt_5_5(tmp_path):
+    agent = _make_agent(tmp_path, model="openai/gpt-5.5")
+    agent.api_mode = "codex_responses"
+    hint = agent._codex_silent_hang_hint(model="openai/gpt-5.5")
+    assert hint is not None
+
+
+def test_hint_fires_for_gpt_5_5_codex_suffix(tmp_path):
+    agent = _make_agent(tmp_path, model="gpt-5.5-codex")
+    agent.api_mode = "codex_responses"
+    hint = agent._codex_silent_hang_hint(model="gpt-5.5-codex")
+    assert hint is not None
+
+
+def test_hint_fires_when_model_arg_omitted(tmp_path):
+    """The helper falls back to ``self.model`` when ``model=`` not passed."""
+    agent = _make_agent(tmp_path)
+    agent.api_mode = "codex_responses"
+    hint = agent._codex_silent_hang_hint()
+    assert hint is not None
+
+
+# ── negative cases: hint stays None ────────────────────────────────────────
+
+
+def test_hint_skipped_for_gpt_5_4_codex(tmp_path):
+    """gpt-5.4-codex is the recommended workaround — must not trigger."""
+    agent = _make_agent(tmp_path, model="gpt-5.4-codex")
+    agent.api_mode = "codex_responses"
+    assert agent._codex_silent_hang_hint(model="gpt-5.4-codex") is None
+
+
+def test_hint_skipped_for_gpt_5_50_false_positive(tmp_path):
+    """``gpt-5.50`` (hypothetical future SKU) must not regex-match gpt-5.5."""
+    agent = _make_agent(tmp_path, model="gpt-5.50")
+    agent.api_mode = "codex_responses"
+    assert agent._codex_silent_hang_hint(model="gpt-5.50") is None
+
+
+def test_hint_skipped_for_non_codex_api_mode(tmp_path):
+    """Hint only fires on the Codex Responses path."""
+    agent = _make_agent(tmp_path)
+    agent.api_mode = "chat_completions"
+    assert agent._codex_silent_hang_hint(model="gpt-5.5") is None
+
+
+def test_hint_skipped_for_non_codex_provider(tmp_path):
+    """Same model on a non-Codex provider does not trigger."""
+    agent = _make_agent(
+        tmp_path,
+        provider="openrouter",
+        base_url="https://openrouter.ai/api/v1",
+        model="openai/gpt-5.5",
+    )
+    agent.api_mode = "codex_responses"
+    assert agent._codex_silent_hang_hint(model="openai/gpt-5.5") is None
+
+
+def test_hint_skipped_for_empty_model(tmp_path):
+    """Explicit empty string ``model`` short-circuits the regex."""
+    agent = _make_agent(tmp_path, model="gpt-5.4-codex")  # self.model non-matching
+    agent.api_mode = "codex_responses"
+    # Explicit empty string: regex won't match
+    assert agent._codex_silent_hang_hint(model="") is None
+    # model=None falls back to self.model which is gpt-5.4-codex, also no match
+    assert agent._codex_silent_hang_hint(model=None) is None
+
+
+def test_hint_skipped_for_unrelated_model_on_codex(tmp_path):
+    agent = _make_agent(tmp_path, model="gpt-4-turbo")
+    agent.api_mode = "codex_responses"
+    assert agent._codex_silent_hang_hint(model="gpt-4-turbo") is None