diff --git a/litellm/proxy/guardrails/_content_utils.py b/litellm/proxy/guardrails/_content_utils.py
index 6cdf49818e6..8861a9e3bbc 100644
--- a/litellm/proxy/guardrails/_content_utils.py
+++ b/litellm/proxy/guardrails/_content_utils.py
@@ -34,6 +34,12 @@ def is_text_content_call_type(call_type: str) -> bool:
 
 TEXT_PART_TYPES: FrozenSet[str] = frozenset({"text", "input_text", "output_text"})
 
+# Responses-API item types whose ``output`` field carries user/tool text
+# that guardrails should inspect.  ``function_call_output`` is the
+# built-in shape; ``custom_tool_call_output`` is the custom-tool
+# counterpart (see ``ChatCompletionCustomToolCallOutput``).
+_OUTPUT_ITEM_TYPES: frozenset[str] = frozenset({"function_call_output", "custom_tool_call_output"})
+
 
 def _iter_text_parts_in_content(content: Any) -> Iterator[str]:
     """Yield text fragments from a ``message.content`` value (string or
@@ -72,7 +78,7 @@ def _coerce_input_to_messages(input_value: Any) -> List[Dict[str, Any]]:
                 messages.append({"role": item.get("role") or "user", "content": [item]})
             elif "content" in item:
                 messages.append({"role": item.get("role") or "user", "content": item["content"]})
-            elif item.get("type") == "function_call_output" and "output" in item:
+            elif item.get("type") in _OUTPUT_ITEM_TYPES and "output" in item:
                 messages.append({"role": item.get("role") or "tool", "content": item["output"]})
     return messages
 
@@ -157,7 +163,7 @@ def walk_user_text(data: Dict[str, Any], visit: Callable[[str], str]) -> int:
                         input_value[idx] = {**item, "text": visit(item["text"])}
                 elif "content" in item:
                     item["content"] = _rewrite_content(item["content"])
-                elif item.get("type") == "function_call_output" and "output" in item:
+                elif item.get("type") in _OUTPUT_ITEM_TYPES and "output" in item:
                     item["output"] = _rewrite_content(item["output"])
         return visited
 
diff --git a/tests/test_litellm/proxy/guardrails/test_content_utils.py b/tests/test_litellm/proxy/guardrails/test_content_utils.py
index 34d92505359..3dfb98c12ea 100644
--- a/tests/test_litellm/proxy/guardrails/test_content_utils.py
+++ b/tests/test_litellm/proxy/guardrails/test_content_utils.py
@@ -524,3 +524,42 @@ def test_apply_redacted_messages_back_skips_input_when_not_string():
     data = {"input": [{"type": "text", "text": "leak"}]}
     apply_redacted_messages_back(data, [{"role": "user", "content": "[REDACTED]"}])
     assert data["input"] == [{"type": "text", "text": "leak"}]
+
+
+# -------------------------------------------------------------------
+# LIT-4302: custom_tool_call_output walking
+# -------------------------------------------------------------------
+
+def test_iter_message_text_walks_custom_tool_call_output():
+    """custom_tool_call_output items should yield their output text."""
+    data = {
+        "input": [
+            {"type": "custom_tool_call_output", "output": "tool-secret"},
+        ]
+    }
+    from litellm.proxy.guardrails._content_utils import iter_message_text
+    texts = list(iter_message_text(data))
+    assert "tool-secret" in texts
+
+
+def test_walk_user_text_redacts_custom_tool_call_output():
+    """walk_user_text should rewrite text inside custom_tool_call_output."""
+    data = {
+        "input": [
+            {"type": "custom_tool_call_output", "output": "PII-data"},
+        ]
+    }
+    count = walk_user_text(data, lambda t: t.replace("PII-data", "[MASKED]"))
+    assert count >= 1
+    assert data["input"][0]["output"] == "[MASKED]"
+
+
+def test_build_inspection_messages_custom_tool_call_output():
+    """build_inspection_messages should include custom_tool_call_output text."""
+    data = {
+        "input": [
+            {"type": "custom_tool_call_output", "output": "custom-tool-leak"},
+        ]
+    }
+    msgs = build_inspection_messages(data)
+    assert any("custom-tool-leak" in m["content"] for m in msgs)