fix(proxy): report a zero cost split only under a zero cost total

The component headers were filled from call-type membership alone, while the
total they sit beside keeps its real value when the read priced normally, so a
breakdown that had not landed by the time headers were built could advertise a
real total next to an all-zero split. The split is now reported as zero only
when the total agrees with it, and is otherwise left absent.

litellm/proxy/common_request_processing.py

@@ -1308,21 +1308,37 @@ _ZERO_COST_BREAKDOWN: Final = CostBreakdownHeaderValues(
 read or management route still finds the whole family rather than a partially populated one."""
 
 
+def _totals_to_zero(response_cost: float | str | None) -> bool:
+    """Whether the total these headers carry is zero, counting a total no route ever priced as one.
+
+    A component split is only reported as zero alongside a total that agrees with it, so a read
+    that did price normally never advertises a real total beside an all-zero split.
+    """
+    if response_cost is None or response_cost == "":
+        return True
+    try:
+        return float(response_cost) == 0.0
+    except (TypeError, ValueError):
+        return False
+
+
 def _get_cost_breakdown_from_logging_obj(
     litellm_logging_obj: LiteLLMLoggingObj | None,
+    response_cost: float | str | None = None,
 ) -> CostBreakdownHeaderValues:
     """Extract discount, margin, and per-component cost information from logging object's cost breakdown.
 
     A non-inference call that priced at zero never records a breakdown, so its components are
     reported as zero here. Any such call that did price normally (retrieving a background response,
-    and the cost poller's read of one) has a stored breakdown and takes the branch below instead.
+    and the cost poller's read of one) reports the breakdown it stored, or nothing at all when the
+    breakdown has not landed yet.
     """
     if not litellm_logging_obj or not hasattr(litellm_logging_obj, "cost_breakdown"):
         return CostBreakdownHeaderValues()
 
     cost_breakdown: Final = litellm_logging_obj.cost_breakdown
     if not cost_breakdown:
-        if litellm_logging_obj.call_type in NON_INFERENCE_CALL_TYPES:
+        if litellm_logging_obj.call_type in NON_INFERENCE_CALL_TYPES and _totals_to_zero(response_cost):
             return _ZERO_COST_BREAKDOWN
         return CostBreakdownHeaderValues()
 
@@ -1467,7 +1483,9 @@ class ProxyBaseLLMRequestProcessing:
         exclude_values: Final = {"", None, "None"}
         hidden_params = hidden_params or {}
 
-        cost_breakdown: Final = _get_cost_breakdown_from_logging_obj(litellm_logging_obj=litellm_logging_obj)
+        cost_breakdown: Final = _get_cost_breakdown_from_logging_obj(
+            litellm_logging_obj=litellm_logging_obj, response_cost=response_cost
+        )
 
         # Calculate updated spend for header (include current response_cost)
         current_spend: Final = user_api_key_dict.spend or 0.0

tests/test_litellm/proxy/test_common_request_processing.py

@@ -5116,6 +5116,27 @@ class TestCostHeadersForCallsPricedAtZero:
 
         assert breakdown == CostBreakdownHeaderValues()
 
+    def test_cost_breakdown_never_zeroes_the_split_under_a_real_total(self):
+        """Reading a background response prices normally, so a breakdown that has not landed by the
+        time headers are built is reported as absent rather than as a zero split contradicting the
+        real total alongside it."""
+        breakdown = _get_cost_breakdown_from_logging_obj(
+            litellm_logging_obj=self._logging_obj(call_type="aget_responses"),
+            response_cost=1.96e-05,
+        )
+
+        assert breakdown == CostBreakdownHeaderValues()
+
+    def test_cost_breakdown_reports_zero_components_under_a_zero_total(self):
+        breakdown = _get_cost_breakdown_from_logging_obj(
+            litellm_logging_obj=self._logging_obj(call_type="aget_responses"),
+            response_cost=0.0,
+        )
+
+        assert breakdown.original_cost == 0.0
+        assert breakdown.input_cost == 0.0
+        assert breakdown.output_cost == 0.0
+
 
 class TestPreCallWithFallbacksOnLocalRateLimit: