diff --git a/api/config.py b/api/config.py
index 1b879bd71..49c8ec9eb 100644
--- a/api/config.py
+++ b/api/config.py
@@ -3522,9 +3522,10 @@ def _main_model_supports_service_tier(
             return False
     else:
         bare_model = raw_model
+    if "codex" in bare_model:
+        return False
     return (
         _is_first_party_model("openai", bare_model)
-        or _is_first_party_model("openai-codex", bare_model)
         or bare_model.startswith(("gpt-", "o1", "o3", "o4"))
     )
 
diff --git a/static/panels.js b/static/panels.js
index 309d33dda..6b63abf43 100644
--- a/static/panels.js
+++ b/static/panels.js
@@ -9701,6 +9701,7 @@ function _mainModelSupportsServiceTier(cfg){
   if(rawModel.slice(0,slash)!=='openai') return false;
   bareModel=rawModel.slice(slash+1);
  }
+ if(bareModel.includes('codex')) return false;
  return bareModel.startsWith('gpt-')||bareModel.startsWith('o1')||bareModel.startsWith('o3')||bareModel.startsWith('o4');
 }
 
diff --git a/tests/test_auxiliary_models_settings.py b/tests/test_auxiliary_models_settings.py
index 308a5fb70..2af243de8 100644
--- a/tests/test_auxiliary_models_settings.py
+++ b/tests/test_auxiliary_models_settings.py
@@ -124,6 +124,7 @@ class TestAuxiliaryModelsJS:
         assert "_mainModelSupportsServiceTier" in PANELS_JS
         assert "rawModel.includes('/')" in helper_body
         assert "rawModel.slice(0,slash)!=='openai'" in helper_body
+        assert "bareModel.includes('codex')" in helper_body
         assert "bareModel.startsWith('gpt-')" in helper_body
         assert "bareModel.startsWith('o4')" in helper_body
         assert "auxAdvancedServiceTier" in modal_body
diff --git a/tests/test_issue4536_service_tier.py b/tests/test_issue4536_service_tier.py
index a0d588b54..3ebaad939 100644
--- a/tests/test_issue4536_service_tier.py
+++ b/tests/test_issue4536_service_tier.py
@@ -69,6 +69,11 @@ class TestIssue4536ServiceTier:
         )
         assert openai_alias_payload == {"service_tier": "priority"}
 
+        codex_payload = config._main_model_request_overrides(
+            {"model": {"provider": "openai-codex", "default": "gpt-5.3-codex", "service_tier": "priority"}},
+        )
+        assert codex_payload == {}
+
         stale_openai_payload = config._main_model_request_overrides(
             {"model": {"provider": "openai", "default": "meta-llama/llama-3.1", "service_tier": "priority"}},
         )