From 85f2ef2c1ac73b9c3bc123aa3968c8fef0cf4734 Mon Sep 17 00:00:00 2001
From: mehmet turac <mehmetturac@gmail.com>
Date: Wed, 2 Sep 2026 11:01:17 +0300
Subject: [PATCH] fix(sdk): use max instead of sum for OpenRouter cost fields

usage.cost already includes upstream_inference_cost on non-BYOK
routes, so summing them double-counts the upstream component.
Use Math.max to pick the correct value for both BYOK (cost=0,
upstream>0) and normal (cost>upstream) routes.

Fixes #1164
---
 sdk/src/impl/__tests__/usage-receipts.test.ts |  3 ++-
 sdk/src/impl/llm.ts                           | 20 +++++++++++--------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/sdk/src/impl/__tests__/usage-receipts.test.ts b/sdk/src/impl/__tests__/usage-receipts.test.ts
index 7e4bba3b96..fb452891d7 100644
--- a/sdk/src/impl/__tests__/usage-receipts.test.ts
+++ b/sdk/src/impl/__tests__/usage-receipts.test.ts
@@ -103,7 +103,8 @@ describe('stream usage receipts', () => {
       },
     ])
     expect(costs).toHaveLength(1)
-    expect(costs[0]).toBeGreaterThan(0)
+    // max(0.01, 0.02) * 1.055 * 100 = 2.11, rounded to 2
+    expect(costs[0]).toBe(2)
     expect(callbackOrder).toEqual(['usage', 'cost'])
   })
 
diff --git a/sdk/src/impl/llm.ts b/sdk/src/impl/llm.ts
index 2ce4cdb443..98d20b20a8 100644
--- a/sdk/src/impl/llm.ts
+++ b/sdk/src/impl/llm.ts
@@ -392,8 +392,10 @@ export async function* promptAiSdkStream(
       | OpenRouterUsageAccounting
       | undefined
     const costOverrideDollars = openrouterUsage
-      ? (openrouterUsage.cost ?? 0) +
-        (openrouterUsage.costDetails?.upstreamInferenceCost ?? 0)
+      ? Math.max(
+          openrouterUsage.cost ?? 0,
+          openrouterUsage.costDetails?.upstreamInferenceCost ?? 0,
+        )
       : undefined
     if (!params.onCostCalculated || !costOverrideDollars) return
     costReported = true
@@ -732,9 +734,10 @@ export async function promptAiSdk(
       const openrouterUsage = providerMetadata.codebuff
         .usage as OpenRouterUsageAccounting
 
-      costOverrideDollars =
-        (openrouterUsage.cost ?? 0) +
-        (openrouterUsage.costDetails?.upstreamInferenceCost ?? 0)
+      costOverrideDollars = Math.max(
+        openrouterUsage.cost ?? 0,
+        openrouterUsage.costDetails?.upstreamInferenceCost ?? 0,
+      )
     }
   }
 
@@ -803,9 +806,10 @@ export async function promptAiSdkStructured<T>(
       const openrouterUsage = providerMetadata.codebuff
         .usage as OpenRouterUsageAccounting
 
-      costOverrideDollars =
-        (openrouterUsage.cost ?? 0) +
-        (openrouterUsage.costDetails?.upstreamInferenceCost ?? 0)
+      costOverrideDollars = Math.max(
+        openrouterUsage.cost ?? 0,
+        openrouterUsage.costDetails?.upstreamInferenceCost ?? 0,
+      )
     }
   }