diff --git a/ui/src/e2e/config-quick-thinking-persistence.e2e.test.ts b/ui/src/e2e/config-quick-thinking-persistence.e2e.test.ts
new file mode 100644
index 000000000000..2e7b760e1475
--- /dev/null
+++ b/ui/src/e2e/config-quick-thinking-persistence.e2e.test.ts
@@ -0,0 +1,105 @@
+// Control UI tests cover Quick Config persistence through the mocked Gateway.
+import { chromium, type Browser } from "playwright";
+import { afterAll, beforeAll, describe, expect, it } from "vitest";
+import {
+  canRunPlaywrightChromium,
+  installMockGateway,
+  resolvePlaywrightChromiumExecutablePath,
+  startControlUiE2eServer,
+  type ControlUiE2eServer,
+  type MockGatewayRequest,
+} from "../test-helpers/control-ui-e2e.ts";
+
+const chromiumExecutablePath = resolvePlaywrightChromiumExecutablePath(chromium.executablePath());
+const chromiumAvailable = canRunPlaywrightChromium(chromiumExecutablePath);
+const allowMissingChromium = process.env.OPENCLAW_UI_E2E_ALLOW_MISSING_CHROMIUM === "1";
+const describeControlUiE2e = chromiumAvailable || !allowMissingChromium ? describe : describe.skip;
+
+let browser: Browser;
+let server: ControlUiE2eServer;
+
+function configResponse(thinkingDefault: "low" | "high", hash: string) {
+  const config = { agents: { defaults: { model: "openai/gpt-5.5", thinkingDefault } } };
+  return {
+    config,
+    hash,
+    issues: [],
+    raw: JSON.stringify(config),
+    valid: true,
+  };
+}
+
+function requestRaw(request: MockGatewayRequest): Record<string, unknown> {
+  const params = request.params;
+  if (!params || typeof params !== "object" || Array.isArray(params)) {
+    throw new Error("Expected config.set params");
+  }
+  return JSON.parse(String((params as Record<string, unknown>).raw)) as Record<string, unknown>;
+}
+
+describeControlUiE2e("Control UI Quick Config thinking persistence mocked Gateway E2E", () => {
+  beforeAll(async () => {
+    if (!chromiumAvailable) {
+      throw new Error(
+        `Playwright Chromium is not installed or cannot start at ${chromiumExecutablePath}. Run \`pnpm --dir ui exec playwright install --with-deps chromium\`, or set OPENCLAW_UI_E2E_ALLOW_MISSING_CHROMIUM=1 only when intentionally skipping this lane.`,
+      );
+    }
+    server = await startControlUiE2eServer();
+    browser = await chromium.launch({ executablePath: chromiumExecutablePath });
+  });
+
+  afterAll(async () => {
+    await browser?.close();
+    await server?.close();
+  });
+
+  it("reads and writes only agents.defaults.thinkingDefault", async () => {
+    const context = await browser.newContext({
+      locale: "en-US",
+      serviceWorkers: "block",
+      viewport: { height: 900, width: 1280 },
+    });
+    const page = await context.newPage();
+    const initialConfig = configResponse("low", "hash-1");
+    const savedConfig = configResponse("high", "hash-2");
+    const gateway = await installMockGateway(page, {
+      methodResponses: {
+        "config.get": initialConfig,
+        "config.set": savedConfig,
+      },
+    });
+
+    try {
+      const response = await page.goto(`${server.baseUrl}config`);
+      expect(response?.status()).toBe(200);
+
+      const modelCard = page.locator(".qs-card--model");
+      const lowButton = modelCard.getByRole("button", { name: "Low", exact: true });
+      await lowButton.waitFor();
+      expect(await lowButton.getAttribute("class")).toContain("qs-segmented__btn--active");
+
+      await modelCard.getByRole("button", { name: "High", exact: true }).click();
+      await page.getByRole("button", { name: "Save", exact: true }).click();
+
+      const raw = requestRaw(await gateway.waitForRequest("config.set"));
+      expect(raw).toEqual({
+        agents: { defaults: { model: "openai/gpt-5.5", thinkingDefault: "high" } },
+      });
+      expect(JSON.stringify(raw)).not.toContain("thinkingLevel");
+      expect(JSON.stringify(raw)).not.toContain("fastMode");
+
+      const freshPage = await context.newPage();
+      await installMockGateway(freshPage, {
+        methodResponses: { "config.get": savedConfig },
+      });
+      await freshPage.goto(`${server.baseUrl}config`);
+      const highButton = freshPage
+        .locator(".qs-card--model")
+        .getByRole("button", { name: "High", exact: true });
+      await highButton.waitFor();
+      expect(await highButton.getAttribute("class")).toContain("qs-segmented__btn--active");
+    } finally {
+      await context.close();
+    }
+  });
+});
diff --git a/ui/src/pages/config/config-page.ts b/ui/src/pages/config/config-page.ts
index a33d889ddbe7..3eeb962d36e0 100644
--- a/ui/src/pages/config/config-page.ts
+++ b/ui/src/pages/config/config-page.ts
@@ -816,7 +816,7 @@ export class ConfigPage extends OpenClawLightDomElement {
     const agentsDefaults = asConfigRecord(asConfigRecord(configObject.agents)?.defaults);
     const model = typeof agentsDefaults?.model === "string" ? agentsDefaults.model : "default";
     const thinkingLevel =
-      typeof agentsDefaults?.thinkingLevel === "string" ? agentsDefaults.thinkingLevel : "off";
+      typeof agentsDefaults?.thinkingDefault === "string" ? agentsDefaults.thinkingDefault : "off";
     const fastMode = agentsDefaults?.fastMode;
     const appConfig = this.context.config.current;
     return renderQuickSettings({
@@ -879,7 +879,7 @@ export class ConfigPage extends OpenClawLightDomElement {
       onSaveConfig: () => void runtimeConfig.save(),
       onApplyConfig: () => void runtimeConfig.apply(),
       onThinkingChange: (level) =>
-        runtimeConfig.patchForm(["agents", "defaults", "thinkingLevel"], level),
+        runtimeConfig.patchForm(["agents", "defaults", "thinkingDefault"], level),
       onFastModeChange: (mode: FastMode) =>
         runtimeConfig.patchForm(["agents", "defaults", "fastMode"], mode),
       onChannelConfigure: () => this.navigate("communications"),