diff --git a/litellm/integrations/custom_guardrail.py b/litellm/integrations/custom_guardrail.py
index 502c3cc95e0..5220dc576fc 100644
--- a/litellm/integrations/custom_guardrail.py
+++ b/litellm/integrations/custom_guardrail.py
@@ -145,6 +145,16 @@ def _unified_hook_fields(guardrail: "CustomGuardrail", request_data: Mapping[str
     }
 
 
+def _inspected_choice_index(request_data: Mapping[str, object]) -> int | None:
+    """The choice this round inspected, as the OpenAI guardrail handler labelled it.
+
+    Read behind a type guard: the key rides on the request body, so anything reaching
+    here that is not a plain int was not written by that handler.
+    """
+    labelled: Final = request_data.get("guardrail_choice_index")
+    return labelled if isinstance(labelled, int) and not isinstance(labelled, bool) else None
+
+
 def _instance_attributes(value: object) -> Mapping[str, object]:
     return vars(value)
 
@@ -1414,7 +1424,7 @@ class CustomGuardrail(CustomLogger):
             end_time=end_time,
             duration=duration,
             masked_entity_count=masked_entity_count,
-            choice_index=request_data.get("guardrail_choice_index"),
+            choice_index=_inspected_choice_index(request_data),
             **(tracing_detail or {}),
         )
 
diff --git a/litellm/proxy/litellm_pre_call_utils.py b/litellm/proxy/litellm_pre_call_utils.py
index 8dc7501bc3b..ee072fd5f80 100644
--- a/litellm/proxy/litellm_pre_call_utils.py
+++ b/litellm/proxy/litellm_pre_call_utils.py
@@ -794,6 +794,26 @@ def _strip_client_pricing_overrides(data: dict[str, object]) -> None:
         )
 
 
+# ``guardrail_choice_index`` is written by the OpenAI guardrail handler around each
+# per-choice inspection round and read by guardrail spend logs as fact; a client value
+# has no legitimate meaning and no key or team setting keeps it.
+_GUARDRAIL_RESERVED_REQUEST_FIELDS: Final = frozenset({"guardrail_choice_index"})
+
+
+def _strip_guardrail_reserved_fields(
+    data: dict[str, object],  # mutable-ok: strips in place on the request body the pre-call pipeline threads through
+) -> None:
+    """Drop the guardrail-owned per-choice label from the client request body."""
+    stripped: Final = tuple(sorted(field for field in _GUARDRAIL_RESERVED_REQUEST_FIELDS if field in data))
+    for field in stripped:
+        data.pop(field, None)
+    if stripped:
+        verbose_proxy_logger.debug(
+            "Stripped guardrail-owned fields from request body: %s. The proxy writes these per round.",
+            ", ".join(stripped),
+        )
+
+
 def _strip_router_reserved_metadata(
     data: dict[str, object],  # mutable-ok: strips in place on the request body the pre-call pipeline threads through
 ) -> None:
@@ -2650,6 +2670,7 @@ async def add_litellm_data_to_request(
     if not _key_or_team_allows_client_pricing_override(user_api_key_dict):
         _strip_client_pricing_overrides(data)
     _strip_router_reserved_metadata(data)
+    _strip_guardrail_reserved_fields(data)
 
     # Same reason as the strips above: runs after the metadata string-to-dict parse
     # so JSON-string metadata cannot smuggle callback credentials past the dict guard.
diff --git a/tests/unit/proxy/guardrails/test_guardrail_choice_index_label.py b/tests/unit/proxy/guardrails/test_guardrail_choice_index_label.py
new file mode 100644
index 00000000000..45f69ad03d8
--- /dev/null
+++ b/tests/unit/proxy/guardrails/test_guardrail_choice_index_label.py
@@ -0,0 +1,73 @@
+"""The per-choice label on guardrail spend logs is proxy-owned, never caller-supplied.
+
+`guardrail_choice_index` names which choice a guardrail round inspected. The OpenAI
+handler writes it around each round; `StandardLoggingGuardrailInformation` reads it and
+spend logs persist it. A caller putting the key in its own request body would otherwise
+have that value stored verbatim, with any type or size, on every guardrail row of the
+request.
+"""
+
+from typing import Final
+from unittest.mock import MagicMock
+
+import pytest
+from fastapi import Request
+
+from litellm.integrations.custom_guardrail import CustomGuardrail
+from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy.litellm_pre_call_utils import add_litellm_data_to_request
+
+
+def _request_mock() -> Request:
+    request_mock = MagicMock(spec=Request)
+    request_mock.url = MagicMock()
+    request_mock.url.path = "/v1/chat/completions"
+    request_mock.url.__str__.return_value = "http://localhost/v1/chat/completions"
+    request_mock.method = "POST"
+    request_mock.query_params = {}
+    request_mock.headers = {"Content-Type": "application/json"}
+    request_mock.client = MagicMock()
+    request_mock.client.host = "127.0.0.1"
+    return request_mock
+
+
+def _logged_choice_index(request_data: dict[str, object]) -> object:
+    guardrail: Final = CustomGuardrail(guardrail_name="choice-label-test")
+    guardrail.add_standard_logging_guardrail_information_to_request_data(
+        guardrail_json_response={},
+        request_data=request_data,
+        guardrail_status="success",
+    )
+    metadata: Final = request_data["metadata"]
+    assert isinstance(metadata, dict)
+    rows: Final = metadata["standard_logging_guardrail_information"]
+    assert isinstance(rows, list)
+    return rows[0]["choice_index"]
+
+
+@pytest.mark.asyncio
+async def test_proxy_drops_a_caller_supplied_choice_index() -> None:
+    data: Final[dict[str, object]] = {
+        "model": "gpt-4",
+        "messages": [{"role": "user", "content": "hi"}],
+        "guardrail_choice_index": "x" * 4096,
+    }
+
+    updated: Final = await add_litellm_data_to_request(
+        data=data,
+        request=_request_mock(),
+        user_api_key_dict=UserAPIKeyAuth(api_key="hashed-key"),
+        proxy_config=MagicMock(),
+        general_settings={},
+        version="test-version",
+    )
+
+    assert "guardrail_choice_index" not in updated
+
+
+def test_a_non_integer_label_is_not_logged() -> None:
+    assert _logged_choice_index({"guardrail_choice_index": "1; drop"}) is None
+
+
+def test_an_integer_label_is_logged() -> None:
+    assert _logged_choice_index({"guardrail_choice_index": 1}) == 1