diff --git a/litellm/llms/openai/responses/guardrail_translation/handler.py b/litellm/llms/openai/responses/guardrail_translation/handler.py
index 1ab4811b8a0..9739ca95089 100644
--- a/litellm/llms/openai/responses/guardrail_translation/handler.py
+++ b/litellm/llms/openai/responses/guardrail_translation/handler.py
@@ -209,7 +209,7 @@ _TOOL_CALL_PAYLOAD_EVENT_TYPES: Final = _TOOL_CALL_PAYLOAD_DELTA_EVENT_TYPES | f
 )
 _OUTPUT_ITEM_EVENT_TYPES: Final = frozenset({"response.output_item.added", "response.output_item.done"})
 _PATCHABLE_ITEM_FIELDS: Final[Mapping[str, str]] = MappingProxyType(
-    {"function_call_output": "output", "message": "content"}
+    {"function_call_output": "output", "custom_tool_call_output": "output", "message": "content"}
 )
 
 _EMPTY_RESPONSES_REQUEST: Final[ResponsesAPIOptionalRequestParams] = {}
diff --git a/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py b/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
index c714b5d378a..ea58a48a3d5 100644
--- a/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
+++ b/tests/test_litellm/llms/openai/responses/test_openai_responses_guardrail_handler.py
@@ -2223,6 +2223,56 @@ class TestStructuredMessagesWriteBack:
         }
         assert result["input"][3] == {"role": "user", "content": "What is the codename?"}
 
+    @pytest.mark.asyncio
+    async def test_codex_custom_tool_items_survive_tool_output_compression(self):
+        handler = OpenAIResponsesHandler()
+        additional_tools_item = {
+            "type": "additional_tools",
+            "tools": [{"type": "custom", "name": "exec", "description": "Run a JavaScript snippet"}],
+        }
+        reasoning_item = {
+            "id": "rs_456",
+            "type": "reasoning",
+            "summary": [],
+            "encrypted_content": "gAAAAA-signed-reasoning",
+        }
+        custom_tool_call_item = {
+            "id": "ctc_456",
+            "type": "custom_tool_call",
+            "call_id": "call_exec",
+            "name": "exec",
+            "input": 'const r = await tools.exec_command({"cmd": "cat memo.txt"});\ntext(r.output);',
+            "status": "completed",
+        }
+        data = {
+            "model": "gpt-5.6",
+            "input": [
+                additional_tools_item,
+                {"role": "user", "content": "What is the codename?"},
+                reasoning_item,
+                custom_tool_call_item,
+                {
+                    "type": "custom_tool_call_output",
+                    "call_id": "call_exec",
+                    "output": [
+                        {"type": "input_text", "text": "Script completed\nOutput:\n"},
+                        {"type": "input_text", "text": "memo " * 400},
+                    ],
+                },
+            ],
+        }
+
+        result = await handler.process_input_messages(data, ToolOutputRewriteGuardrail())
+
+        assert result["input"][0] is additional_tools_item
+        assert result["input"][1] == {"role": "user", "content": "What is the codename?"}
+        assert result["input"][2] is reasoning_item
+        assert result["input"][3] is custom_tool_call_item
+        assert result["input"][4]["type"] == "custom_tool_call_output"
+        assert result["input"][4]["call_id"] == "call_exec"
+        assert COMPRESSED_MARKER in str(result["input"][4]["output"])
+        assert len(result["input"]) == 5
+
     @pytest.mark.asyncio
     async def test_web_search_call_item_preserved_verbatim(self):
         handler = OpenAIResponsesHandler()