diff --git a/scripts/paid-test-durations.json b/scripts/paid-test-durations.json
index d120102f4..bc02a74d5 100644
--- a/scripts/paid-test-durations.json
+++ b/scripts/paid-test-durations.json
@@ -141,6 +141,7 @@
       "test/skill-e2e-coverage-audit.test.ts": 1000,
       "test/skill-e2e-cso.test.ts": 253498,
       "test/skill-e2e-deploy.test.ts": 1000,
+      "test/skill-e2e-design-model-smoke.test.ts": 90000,
       "test/skill-e2e-design.test.ts": 817000,
       "test/skill-e2e-design.test.ts#design-consultation-core": 159257,
       "test/skill-e2e-design.test.ts#design-consultation-existing": 175607,
diff --git a/test/skill-e2e-design-model-smoke.test.ts b/test/skill-e2e-design-model-smoke.test.ts
new file mode 100644
index 000000000..4f8c9a57e
--- /dev/null
+++ b/test/skill-e2e-design-model-smoke.test.ts
@@ -0,0 +1,41 @@
+/**
+ * Design model smoke (E5, periodic): runs design/scripts/live-model-check.ts,
+ * which sends the design binary's real request bodies with the DEFAULT
+ * models (overrides are ignored), so a retired or unentitled default fails
+ * here before users hit it. Without OPENAI_API_KEY the case is a Bun skip:
+ * the report lists it as SKIPPED with zero coverage credit, never a pass.
+ * With a key, exit 0 passes; exit 2 (the script saw no key) and every other
+ * exit fail with the script's output attached.
+ */
+import { describe, test, expect } from 'bun:test';
+import { spawnSync } from 'child_process';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { e2eTierEnabled } from './helpers/e2e-gate';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const CASE = 'design-model-smoke';
+const KEY_PRESENT = !!process.env.OPENAI_API_KEY?.trim();
+const CHECK_MS = 400_000;
+if (e2eTierEnabled('periodic') && !KEY_PRESENT) {
+  process.stderr.write(`\n${CASE}: SKIPPED: OPENAI_API_KEY is not set; the design model defaults were not checked (no coverage)\n`);
+}
+
+describe.skipIf(!e2eTierEnabled('periodic') || !KEY_PRESENT)('design live model defaults (E5)', () => {
+  test(CASE, () => {
+    const home = fs.mkdtempSync(path.join(os.tmpdir(), 'design-model-smoke-'));
+    try {
+      const run = spawnSync(process.execPath, ['run', 'design/scripts/live-model-check.ts'], {
+        cwd: ROOT, encoding: 'utf8', timeout: CHECK_MS,
+        env: { ...process.env, HOME: home, GSTACK_HOME: path.join(home, '.gstack') },
+      });
+      const output = `${run.stdout ?? ''}${run.stderr ?? ''}`.trim();
+      console.log(output);
+      if (run.status === 2) throw new Error(`live-model-check saw no OPENAI_API_KEY although the test had one; nothing was checked:\n${output}`);
+      expect(run.status, output).toBe(0);
+    } finally {
+      fs.rmSync(home, { recursive: true, force: true });
+    }
+  }, CHECK_MS + 10_000);
+});