fix: bill the serving provider's fee on the USD-cost path

The USD-cost path (and the litellm pricing fallback) resolved the
provider fee via get_provider_for_model(model_id)[0] — the best-ranked
provider for the alias, not the one that served. Settlement callers in
the upstream handlers now pass their own provider_fee through
adjust_payment_for_tokens / get_x_cashu_cost into calculate_cost; the
string-derived fallback remains for callers without a serving provider.
Configured model pricing is unaffected (the fee is already baked into
cached pricing).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

routstr/auth.py

@@ -775,6 +775,7 @@ async def adjust_payment_for_tokens(
     session: AsyncSession,
     deducted_max_cost: int,
     model_obj: "Model | None" = None,
+    provider_fee: float | None = None,
 ) -> dict:
     """
     Adjusts the payment based on token usage in the response.
@@ -869,7 +870,9 @@ async def adjust_payment_for_tokens(
                     extra={"error": str(e), "fee_msats": fee_msats},
                 )
 
-    match await calculate_cost(response_data, deducted_max_cost, model_obj):
+    match await calculate_cost(
+        response_data, deducted_max_cost, model_obj, provider_fee
+    ):
         case MaxCostData() as cost:
             logger.debug(
                 "Using max cost data (no token adjustment)",

routstr/payment/cost_calculation.py

@@ -71,6 +71,7 @@ async def calculate_cost(
     response_data: dict,
     max_cost: int,
     model_obj: "Model | None" = None,
+    provider_fee: float | None = None,
 ) -> CostData | MaxCostData | CostDataError:
     """Calculate the cost of an API request based on token usage.
 
@@ -81,6 +82,11 @@ async def calculate_cost(
             its pricing is billed directly; without it, pricing is re-derived
             from the response's model string via the alias map, which resolves
             to the best-ranked candidate — not necessarily the serving one.
+        provider_fee: The serving provider's fee multiplier, applied on the
+            USD-cost path and the litellm pricing fallback (configured model
+            pricing already carries the fee baked in). Without it, the fee is
+            re-derived from the response's model string, which yields the
+            best-ranked provider's fee.
 
     Returns:
         Cost data or error information
@@ -186,6 +192,7 @@ async def calculate_cost(
                 cache_creation_tokens,
                 output_tokens,
                 response_data,
+                provider_fee,
             )
         except Exception as e:
             logger.warning(
@@ -199,7 +206,7 @@ async def calculate_cost(
 
     # Fall back to token-based pricing
     try:
-        pricing_rates = _get_pricing_rates(response_data, model_obj)
+        pricing_rates = _get_pricing_rates(response_data, model_obj, provider_fee)
     except ValueError as e:
         return CostDataError(message=str(e), code="pricing_error")
 
@@ -317,6 +324,7 @@ def _resolve_usd_cost(usage_data: dict, response_data: dict) -> float:
 def _get_pricing_rates(
     response_data: dict,
     model_obj: "Model | None" = None,
+    provider_fee: float | None = None,
 ) -> tuple[float, float, float, float] | None:
     """Get configured rates, falling back to LiteLLM's model cost map.
 
@@ -380,6 +388,7 @@ def _get_pricing_rates(
         if input_usd <= 0 or output_usd <= 0:
             raise ValueError(f"Incomplete LiteLLM pricing for model: {pricing_model}")
 
+        if provider_fee is None:
             provider_fee = _resolve_provider_fee(response_model)
         usd_per_sat = sats_usd_price()
         mspp_1k = input_usd * provider_fee * 1_000_000.0 / usd_per_sat
@@ -441,8 +450,10 @@ def _calculate_from_usd_cost(
     cache_creation_tokens: int,
     output_tokens: int,
     response_data: dict,
+    provider_fee: float | None = None,
 ) -> CostData:
     """Calculate cost from USD figures, deriving input/output split from tokens."""
+    if provider_fee is None:
         provider_fee = _resolve_provider_fee(response_data.get("model", ""))
     usd_cost = usd_cost * provider_fee
     input_usd = input_usd * provider_fee

routstr/upstream/base.py

@@ -841,6 +841,7 @@ class BaseUpstreamProvider:
                             new_session,
                             max_cost_for_model,
                             model_obj,
+                            self.provider_fee,
                         )
                         usage_finalized = True
                     except Exception:
@@ -1014,6 +1015,7 @@ class BaseUpstreamProvider:
                                 session,
                                 max_cost_for_model,
                                 model_obj,
+                                self.provider_fee,
                             )
                             usage_finalized = True
                         except Exception as e:
@@ -1158,6 +1160,7 @@ class BaseUpstreamProvider:
                 session,
                 deducted_max_cost,
                 model_obj,
+                self.provider_fee,
             )
 
             await session.refresh(key)
@@ -1298,6 +1301,7 @@ class BaseUpstreamProvider:
                             new_session,
                             max_cost_for_model,
                             model_obj,
+                            self.provider_fee,
                         )
                         usage_finalized = True
                     except Exception:
@@ -1428,6 +1432,7 @@ class BaseUpstreamProvider:
                                 session,
                                 max_cost_for_model,
                                 model_obj,
+                                self.provider_fee,
                             )
                             usage_finalized = True
                         except Exception as e:
@@ -1597,6 +1602,7 @@ class BaseUpstreamProvider:
                 session,
                 deducted_max_cost,
                 model_obj,
+                self.provider_fee,
             )
 
             await session.refresh(key)
@@ -1797,6 +1803,7 @@ class BaseUpstreamProvider:
                             new_session,
                             max_cost_for_model,
                             model_obj,
+                            self.provider_fee,
                         )
                         usage_finalized = True
                         return f"event: cost\ndata: {json.dumps({'cost': cost_data})}\n\n".encode()
@@ -1949,6 +1956,7 @@ class BaseUpstreamProvider:
                                     new_session,
                                     max_cost_for_model,
                                     model_obj,
+                                    self.provider_fee,
                                 )
 
                                 self.inject_cost_metadata(
@@ -2022,6 +2030,7 @@ class BaseUpstreamProvider:
                 session,
                 deducted_max_cost,
                 model_obj,
+                self.provider_fee,
             )
 
             self.inject_cost_metadata(response_json, cost_data, key)
@@ -2129,6 +2138,7 @@ class BaseUpstreamProvider:
             session,
             max_cost_for_model,
             model_obj,
+            self.provider_fee,
         )
         self.inject_cost_metadata(response_json, cost_data, key)
 
@@ -2275,6 +2285,7 @@ class BaseUpstreamProvider:
                             new_session,
                             max_cost_for_model,
                             model_obj,
+                            self.provider_fee,
                         )
                         usage_finalized = True
                         return (
@@ -2349,6 +2360,7 @@ class BaseUpstreamProvider:
                                     new_session,
                                     max_cost_for_model,
                                     model_obj,
+                                    self.provider_fee,
                                 )
                                 self.inject_cost_metadata(
                                     combined_data, cost_data, fresh_key
@@ -3265,6 +3277,7 @@ class BaseUpstreamProvider:
             response_data,
             max_cost_for_model,
             model_obj,
+            self.provider_fee,
         ):
             case MaxCostData() as cost:
                 logger.debug(

tests/unit/test_messages_litellm_dispatch.py

@@ -502,7 +502,12 @@ async def test_streaming_emits_sse_and_reconciles_cost_at_end() -> None:
     captured_cost_call: dict[str, Any] = {}
 
     async def fake_adjust(
-        fresh_key: Any, combined_data: Any, sess: Any, max_cost: int, usage: Any = None
+        fresh_key: Any,
+        combined_data: Any,
+        sess: Any,
+        max_cost: int,
+        model_obj: Any = None,
+        provider_fee: Any = None,
     ) -> dict:
         captured_cost_call["combined_data"] = combined_data
         captured_cost_call["max_cost"] = max_cost
@@ -591,7 +596,12 @@ async def test_streaming_handles_iterator_yielding_raw_sse_bytes() -> None:
     captured: dict[str, Any] = {}
 
     async def fake_adjust(
-        fresh_key: Any, combined_data: Any, sess: Any, max_cost: int, usage: Any = None
+        fresh_key: Any,
+        combined_data: Any,
+        sess: Any,
+        max_cost: int,
+        model_obj: Any = None,
+        provider_fee: Any = None,
     ) -> dict:
         captured["combined_data"] = combined_data
         return fake_cost

tests/unit/test_settlement_identity.py

@@ -88,6 +88,45 @@ async def test_string_fallback_still_prices_without_model_obj() -> None:
     assert result.total_msats == 2_000
 
 
+@pytest.mark.asyncio
+async def test_usd_cost_path_applies_given_provider_fee() -> None:
+    """The USD-cost path bills the serving provider's fee when supplied."""
+    from unittest.mock import Mock
+
+    response = dict(RESPONSE)
+    response["usage"] = dict(RESPONSE["usage"], cost=0.001)  # type: ignore[arg-type]
+
+    best_ranked = Mock(provider_fee=1.0)
+    with patch(
+        "routstr.proxy.get_provider_for_model", return_value=[best_ranked]
+    ):
+        result = await calculate_cost(
+            response, max_cost=100_000, model_obj=SERVED, provider_fee=1.5
+        )
+
+    assert isinstance(result, CostData)
+    # 0.001 USD * fee 1.5 / 0.0005 USD-per-sat = 3 sats = 3000 msats.
+    assert result.total_msats == 3_000
+
+
+@pytest.mark.asyncio
+async def test_usd_cost_path_falls_back_to_best_ranked_fee() -> None:
+    """Without a supplied fee, the alias-map provider lookup still applies."""
+    from unittest.mock import Mock
+
+    response = dict(RESPONSE)
+    response["usage"] = dict(RESPONSE["usage"], cost=0.001)  # type: ignore[arg-type]
+
+    best_ranked = Mock(provider_fee=2.0)
+    with patch(
+        "routstr.proxy.get_provider_for_model", return_value=[best_ranked]
+    ):
+        result = await calculate_cost(response, max_cost=100_000)
+
+    assert isinstance(result, CostData)
+    assert result.total_msats == 4_000
+
+
 @pytest.mark.asyncio
 async def test_x_cashu_cost_uses_served_model_not_upstream_echo() -> None:
     """``get_x_cashu_cost`` bills the routed model, not the raw model echo.