diff --git a/extensions/openrouter/index.test.ts b/extensions/openrouter/index.test.ts
index 85dd7ba8174b..6dc5fefb3413 100644
--- a/extensions/openrouter/index.test.ts
+++ b/extensions/openrouter/index.test.ts
@@ -791,6 +791,57 @@ describe("openrouter provider hooks", () => {
     }
   });
 
+  it("falls back to streamed cost estimate when generation metadata response is oversized", async () => {
+    const provider = await registerSingleProviderPlugin(openrouterPlugin);
+    // Body exceeds the 16 MiB cap; readProviderJsonResponse must reject it and
+    // applyOpenRouterBilledCost must fall back to the streamed estimate.
+    const oversizedBody = new ReadableStream<Uint8Array>({
+      start(controller) {
+        controller.enqueue(new Uint8Array(16 * 1024 * 1024 + 1).fill(0x78));
+        controller.close();
+      },
+    });
+    const fetchMock = vi.fn(async (url: string) => {
+      expect(url).toBe("https://openrouter.ai/api/v1/generation?id=gen-oversized-1");
+      return new Response(oversizedBody, {
+        headers: { "Content-Type": "application/json" },
+        status: 200,
+      });
+    });
+    vi.stubGlobal("fetch", fetchMock);
+    const baseStreamFn = vi.fn(() =>
+      createOpenRouterDoneStream({ responseId: "gen-oversized-1", totalCost: 0.001 }),
+    );
+
+    try {
+      const wrapped = provider.wrapStreamFn?.({
+        provider: "openrouter",
+        modelId: "openrouter/auto",
+        streamFn: baseStreamFn,
+      } as never);
+      if (!wrapped) {
+        throw new Error("expected OpenRouter wrapper");
+      }
+      const stream = await wrapped(
+        {
+          provider: "openrouter",
+          api: "openai-completions",
+          id: "openrouter/auto",
+          baseUrl: "https://openrouter.ai/api/v1",
+          compat: {},
+        } as never,
+        { messages: [] } as never,
+        { apiKey: "or-test-key" } as never,
+      );
+      const message = await stream.result();
+
+      expect(fetchMock).toHaveBeenCalledOnce();
+      expect(message.usage.cost.total).toBe(0.001);
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
+
   it("does not fetch generation metadata for custom OpenRouter-compatible routes", async () => {
     const provider = await registerSingleProviderPlugin(openrouterPlugin);
     const fetchMock = vi.fn();
diff --git a/extensions/openrouter/stream.ts b/extensions/openrouter/stream.ts
index fbfa8a999075..afc1fecf153a 100644
--- a/extensions/openrouter/stream.ts
+++ b/extensions/openrouter/stream.ts
@@ -9,6 +9,7 @@ import type { ProviderWrapStreamFnContext } from "openclaw/plugin-sdk/plugin-ent
 import {
   assertOkOrThrowHttpError,
   fetchWithTimeoutGuarded,
+  readProviderJsonResponse,
 } from "openclaw/plugin-sdk/provider-http";
 import { OPENROUTER_THINKING_STREAM_HOOKS } from "openclaw/plugin-sdk/provider-stream-family";
 import {
@@ -124,7 +125,12 @@ async function fetchOpenRouterGenerationTotalCost(params: {
   );
   try {
     await assertOkOrThrowHttpError(response, "OpenRouter generation metadata request failed");
-    return readOpenRouterTotalCost((await response.json()) as OpenRouterGenerationResponse);
+    return readOpenRouterTotalCost(
+      await readProviderJsonResponse<OpenRouterGenerationResponse>(
+        response,
+        "openrouter.generation-cost",
+      ),
+    );
   } finally {
     await release();
   }