diff --git a/litellm/llms/pass_through/guardrail_translation/handler.py b/litellm/llms/pass_through/guardrail_translation/handler.py
index 57044b96f44..ac91b7bd260 100644
--- a/litellm/llms/pass_through/guardrail_translation/handler.py
+++ b/litellm/llms/pass_through/guardrail_translation/handler.py
@@ -63,25 +63,21 @@ _REPLY_NESTED_FIELDS: Final = MappingProxyType(
     }
 )
 _REPLY_MODEL_OUTPUT_FIELDS: Final = frozenset(("args", "arguments", "input", "parameters"))
-_REPLY_MARKER_FIELDS: Final = frozenset(
-    (
-        "candidates",
-        "choices",
-        "finish_reason",
-        "object",
-        "output",
-        "predictions",
-        "stop_reason",
-        "usage",
-        "usageMetadata",
-    )
-)
+_REPLY_LIST_FIELDS: Final = ("candidates", "choices", "output", "predictions")
 _IMAGE_REPLY_FIELDS: Final = frozenset(("created", "data"))
 _NO_FIELDS: Final[frozenset[str]] = frozenset()
 
 
 def _is_provider_reply(response: Mapping[str, object]) -> bool:
-    return bool(_REPLY_MARKER_FIELDS & response.keys()) or _IMAGE_REPLY_FIELDS.issubset(response)
+    """Whether a JSON response has the shape of a provider's reply, by the type of the field that names it, since a
+    custom API's JSON can use the same field names."""
+    return (
+        any(isinstance(response.get(field), list) for field in _REPLY_LIST_FIELDS)
+        or isinstance(response.get("object"), str)
+        or (response.get("type") == "message" and "stop_reason" in response)
+        or ("finish_reason" in response and "message" in response)
+        or _IMAGE_REPLY_FIELDS.issubset(response)
+    )
 
 
 def _reply_field_position(name: str, skipped: frozenset[str] | None) -> frozenset[str] | None:
diff --git a/tests/unit/llms/pass_through/guardrail_translation/test_handler.py b/tests/unit/llms/pass_through/guardrail_translation/test_handler.py
index 43c8ce9cc1a..e028ff2a7bd 100644
--- a/tests/unit/llms/pass_through/guardrail_translation/test_handler.py
+++ b/tests/unit/llms/pass_through/guardrail_translation/test_handler.py
@@ -286,6 +286,9 @@ async def test_post_call_scan_reads_a_field_named_like_the_envelope_in_what_the_
             "4111111111111111",
         ),
         ({"choices": [{"message": {"tool_calls": [{"function": {"arguments": {"n": 5551234567}}}]}}]}, "5551234567"),
+        ({"usage": {}, "customer": {"phone": 5551234567}}, "5551234567"),
+        ({"output": {"card": 4111111111111111}}, "4111111111111111"),
+        ({"type": "message", "phone": 5551234567}, "5551234567"),
     ],
 )
 async def test_post_call_scan_reads_an_integer_in_what_the_model_or_api_wrote(response, expected):
@@ -311,6 +314,7 @@ async def test_post_call_scan_reads_a_field_name_in_what_the_model_or_api_wrote(
         {"created": 1793600123, "data": [{"url": "https://x.example/a.png"}]},
         {"id": "batch_1", "object": "batch", "created_at": 1793600123, "request_counts": {"total": 5551234567}},
         {"predictions": [{"embeddings": {"values": [0.0123456789]}, "total": 5551234567}]},
+        {"finish_reason": "COMPLETE", "message": {"role": "assistant"}, "usage": {"total": 5551234567}},
     ],
 )
 async def test_post_call_scan_leaves_out_the_numbers_of_a_provider_reply(response):