From e94ece85b643517a023d02ca413bbb424b3aaa8c Mon Sep 17 00:00:00 2001
From: Vincent Koc <vincentkoc@ieee.org>
Date: Sat, 25 Jul 2026 19:26:09 +0800
Subject: [PATCH] fix(anthropic): preserve opus fallback pricing

---
 .../anthropic-server-fallback.test.ts         |  7 +++---
 .../providers/anthropic-server-fallback.ts    | 23 ++-----------------
 2 files changed, 6 insertions(+), 24 deletions(-)

diff --git a/packages/ai/src/providers/anthropic-server-fallback.test.ts b/packages/ai/src/providers/anthropic-server-fallback.test.ts
index 0e2d4acc4a49..2788b0856ea0 100644
--- a/packages/ai/src/providers/anthropic-server-fallback.test.ts
+++ b/packages/ai/src/providers/anthropic-server-fallback.test.ts
@@ -21,14 +21,15 @@ describe("Anthropic server-side fallback", () => {
     },
   );
 
-  it("preserves fast-mode pricing when Opus 5 falls back to Opus 4.8", () => {
+  it("preserves requested pricing when Opus 5 falls back to Opus 4.8", () => {
+    const customOpusCost = { input: 12, output: 60, cacheRead: 1.2, cacheWrite: 15 };
     expect(
       resolveAnthropicFallbackServingModelCost({
         requestedModelId: "claude-opus-5",
         servingModelId: "claude-opus-4-8",
-        requestedCost: OPUS_FAST_COST,
+        requestedCost: customOpusCost,
       }),
-    ).toEqual(OPUS_FAST_COST);
+    ).toBe(customOpusCost);
   });
 
   it("keeps requested pricing for an unknown future fallback target", () => {
diff --git a/packages/ai/src/providers/anthropic-server-fallback.ts b/packages/ai/src/providers/anthropic-server-fallback.ts
index 5759817d3824..f3c21ebe3045 100644
--- a/packages/ai/src/providers/anthropic-server-fallback.ts
+++ b/packages/ai/src/providers/anthropic-server-fallback.ts
@@ -20,27 +20,11 @@ export const CLAUDE_OPUS_FALLBACK_MODEL_COST = {
   cacheWrite: 6.25,
 } as const;
 
-const CLAUDE_OPUS_FAST_FALLBACK_MODEL_COST = {
-  input: 10,
-  output: 50,
-  cacheRead: 1,
-  cacheWrite: 12.5,
-} as const;
-
 export type AnthropicFallbackBoundary = {
   fromModel: string | null;
   toModel: string | null;
 };
 
-function isModelCostEqual(left: Model["cost"], right: Model["cost"]): boolean {
-  return (
-    left.input === right.input &&
-    left.output === right.output &&
-    left.cacheRead === right.cacheRead &&
-    left.cacheWrite === right.cacheWrite
-  );
-}
-
 function resolveFallbackModelIdentity(modelId: string | null): string | null {
   if (!modelId?.trim()) {
     return null;
@@ -78,11 +62,8 @@ export function resolveAnthropicFallbackServingModelCost(params: {
   ) {
     return params.requestedCost;
   }
-  if (
-    requestedModelId === "claude-opus-5" &&
-    isModelCostEqual(params.requestedCost, CLAUDE_OPUS_FAST_FALLBACK_MODEL_COST)
-  ) {
-    return CLAUDE_OPUS_FAST_FALLBACK_MODEL_COST;
+  if (requestedModelId && isClaudeOpusFallbackModel(requestedModelId)) {
+    return params.requestedCost;
   }
   return CLAUDE_OPUS_FALLBACK_MODEL_COST;
 }