diff --git a/src/app/v1/_lib/proxy/forwarder.ts b/src/app/v1/_lib/proxy/forwarder.ts
index 47002d6dc..10dc55885 100644
--- a/src/app/v1/_lib/proxy/forwarder.ts
+++ b/src/app/v1/_lib/proxy/forwarder.ts
@@ -135,6 +135,10 @@ function decodeRequestBodyAsJson(body: BodyInit | undefined): Record<string, unk
   }
 }
 
+function isNonRetryableUpstreamRequestError(error: Error): error is ProxyError {
+  return error instanceof ProxyError && (error.statusCode === 400 || error.statusCode === 422);
+}
+
 const OUTBOUND_TRANSPORT_HEADER_BLACKLIST = [
   "content-length",
   "connection",
@@ -1684,6 +1688,13 @@ export class ProxyForwarder {
             }
           }
 
+          if (
+            errorCategory === ErrorCategory.PROVIDER_ERROR &&
+            isNonRetryableUpstreamRequestError(lastError)
+          ) {
+            errorCategory = ErrorCategory.NON_RETRYABLE_CLIENT_ERROR;
+          }
+
           // ⭐ 3. 不可重试的客户端输入错误处理（不计入熔断器，不重试，立即返回）
           if (errorCategory === ErrorCategory.NON_RETRYABLE_CLIENT_ERROR) {
             const detectionResult = await getErrorDetectionResultAsync(lastError);
diff --git a/tests/unit/proxy/proxy-forwarder-retry-limit.test.ts b/tests/unit/proxy/proxy-forwarder-retry-limit.test.ts
index 9ce0e828b..5aa5316ec 100644
--- a/tests/unit/proxy/proxy-forwarder-retry-limit.test.ts
+++ b/tests/unit/proxy/proxy-forwarder-retry-limit.test.ts
@@ -894,6 +894,41 @@ describe("ProxyForwarder - retry limit enforcement", () => {
   });
 });
 
+describe("ProxyForwarder - client request upstream errors", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(categorizeErrorAsync).mockResolvedValue(ErrorCategory.PROVIDER_ERROR);
+  });
+
+  test("upstream 400 should not retry or count against provider circuit breaker", async () => {
+    const session = createSession();
+    const provider = createProvider({
+      providerVendorId: null,
+      maxRetryAttempts: 4,
+    });
+    session.setProvider(provider);
+
+    const doForward = vi.spyOn(
+      ProxyForwarder as unknown as { doForward: (...args: unknown[]) => unknown },
+      "doForward"
+    );
+    doForward.mockImplementationOnce(async () => {
+      throw new ProxyError("Provider returned 400: Bad Request", 400, {
+        body: '{"detail":"Bad Request"}',
+        providerId: provider.id,
+        providerName: provider.name,
+      });
+    });
+
+    await expect(ProxyForwarder.send(session)).rejects.toMatchObject({
+      statusCode: 400,
+    });
+
+    expect(doForward).toHaveBeenCalledTimes(1);
+    expect(mocks.recordFailure).not.toHaveBeenCalled();
+  });
+});
+
 describe("ProxyForwarder - endpoint stickiness on retry", () => {
   beforeEach(() => {
     vi.clearAllMocks();