diff --git a/hermes_cli/models.py b/hermes_cli/models.py
index d7bae9ab09..984685e6c3 100644
--- a/hermes_cli/models.py
+++ b/hermes_cli/models.py
@@ -3185,11 +3185,12 @@ def validate_requested_model(
             if suggestions:
                 suggestion_text = "\n  Similar models: " + ", ".join(f"`{s}`" for s in suggestions)
             return {
-                "accepted": False,
-                "persist": False,
+                "accepted": True,
+                "persist": True,
                 "recognized": False,
                 "message": (
-                    f"Model `{requested}` was not found in the OpenAI Codex model listing."
+                    f"Note: `{requested}` was not found in the OpenAI Codex model listing. "
+                    "It may still work if your ChatGPT/Codex account has access to a newer or hidden model ID."
                     f"{suggestion_text}"
                 ),
             }
diff --git a/tests/hermes_cli/test_openai_codex_model_validation_fallback.py b/tests/hermes_cli/test_openai_codex_model_validation_fallback.py
new file mode 100644
index 0000000000..e33dbe2ba4
--- /dev/null
+++ b/tests/hermes_cli/test_openai_codex_model_validation_fallback.py
@@ -0,0 +1,55 @@
+"""Regression tests for OpenAI Codex model validation when the listing lags behind
+actually usable backend model IDs.
+
+The bug: `/model` and `switch_model()` reject `gpt-5.3-codex-spark` because the
+OpenAI Codex listing omits it, even though direct runtime calls with
+`--provider openai-codex -m gpt-5.3-codex-spark` succeed.
+"""
+
+from unittest.mock import patch
+
+from hermes_cli.model_switch import switch_model
+from hermes_cli.models import validate_requested_model
+
+
+def test_openai_codex_unknown_but_plausible_model_is_accepted_with_warning():
+    """If the Codex listing is incomplete, `/model` should soft-accept the model
+    with a warning instead of hard-rejecting it.
+    """
+    with patch(
+        "hermes_cli.models.provider_model_ids",
+        return_value=["gpt-5.5", "gpt-5.4", "gpt-5.3-codex"],
+    ):
+        result = validate_requested_model("gpt-5.3-codex-spark", "openai-codex")
+
+    assert result["accepted"] is True
+    assert result["persist"] is True
+    assert result["recognized"] is False
+    assert "gpt-5.3-codex-spark" in result["message"]
+    assert "OpenAI Codex model listing" in result["message"]
+    assert "Similar models" in result["message"]
+    assert "gpt-5.3-codex" in result["message"]
+
+
+def test_switch_model_allows_openai_codex_model_missing_from_listing():
+    """switch_model() should succeed for Codex models that the runtime accepts
+    even when the listing has not caught up yet.
+    """
+    with patch(
+        "hermes_cli.models.provider_model_ids",
+        return_value=["gpt-5.5", "gpt-5.4", "gpt-5.3-codex"],
+    ):
+        result = switch_model(
+            "gpt-5.3-codex-spark",
+            current_provider="openai-codex",
+            current_model="gpt-5.4",
+            current_base_url="",
+            current_api_key="",
+            user_providers=None,
+        )
+
+    assert result.success is True
+    assert result.new_model == "gpt-5.3-codex-spark"
+    assert result.target_provider == "openai-codex"
+    assert result.warning_message
+    assert "OpenAI Codex model listing" in result.warning_message