diff --git a/src/shared/utils/apiKeyPolicy.ts b/src/shared/utils/apiKeyPolicy.ts
index 1d674af112..2d14ca89fe 100644
--- a/src/shared/utils/apiKeyPolicy.ts
+++ b/src/shared/utils/apiKeyPolicy.ts
@@ -321,6 +321,33 @@ export async function enforceApiKeyPolicy(
     }
   }
 
+  // ── Check 2.9: qtSd models require a quota-pool allocation ──
+  //
+  // quotaShared-* (qtSd/<group>/<provider>/<model>) virtual models are pool-gated:
+  // a key that is NOT allocated to any quota pool (empty allowedQuotas) must not be
+  // able to call them — otherwise an ordinary key could route through someone
+  // else's shared quota. Only allocated keys (allowedQuotas non-empty, further
+  // validated against their pool scope in Check 3 below) may use qtSd models.
+  if (
+    modelStr &&
+    isQuotaModelName(modelStr) &&
+    !(Array.isArray(apiKeyInfo.allowedQuotas) && apiKeyInfo.allowedQuotas.length > 0)
+  ) {
+    const notAllocatedBody = buildErrorBody(
+      HTTP_STATUS.FORBIDDEN,
+      `Model "${modelStr}" requires a quota-pool allocation; this API key is not allocated to any quota pool`
+    );
+    notAllocatedBody.error.code = "QUOTA_NOT_ALLOCATED";
+    return {
+      apiKey,
+      apiKeyInfo,
+      rejection: new Response(JSON.stringify(notAllocatedBody), {
+        status: HTTP_STATUS.FORBIDDEN,
+        headers: { "Content-Type": "application/json" },
+      }),
+    };
+  }
+
   // ── Check 3: Quota-exclusive enforcement (Phase B4) ──
   //
   // When a key has allowedQuotas its access is governed exclusively by the
diff --git a/tests/unit/apikeypolicy-quota-only.test.ts b/tests/unit/apikeypolicy-quota-only.test.ts
index 07dfd9961f..3c2641cb10 100644
--- a/tests/unit/apikeypolicy-quota-only.test.ts
+++ b/tests/unit/apikeypolicy-quota-only.test.ts
@@ -236,6 +236,26 @@ test("key with empty allowedQuotas is subject to normal model restriction checks
   assert.notEqual(body.error.code, "QUOTA_ONLY", "normal key rejection must NOT use QUOTA_ONLY code");
 });
 
+test("non-quota key (empty allowedQuotas) requesting a qtSd model is rejected 403 QUOTA_NOT_ALLOCATED", async () => {
+  // A normal key with NO quota allocation must NOT route through a shared quota pool.
+  const created = await apiKeysDb.createApiKey("Normal Key No Quota", "machine-b4-noalloc");
+  // (no allowedQuotas set → empty array)
+
+  const policy = await loadPolicy("b4-quota-noalloc");
+  const qtSdModel = quotaModelName("AnyGroup", "codex", "gpt-5.5");
+
+  const blocked = await policy.enforceApiKeyPolicy(makeRequest(created.key), qtSdModel);
+  assert.ok(blocked.rejection, "non-quota key must be blocked from qtSd models");
+  assert.equal(blocked.rejection.status, 403);
+  const body = await readBody(blocked.rejection);
+  assert.equal(body.error.code, "QUOTA_NOT_ALLOCATED", "must use QUOTA_NOT_ALLOCATED code");
+  assert.match(body.error.message, /quota-pool allocation/);
+
+  // Sanity: the same key can still use a normal (non-qtSd) model freely.
+  const allowed = await policy.enforceApiKeyPolicy(makeRequest(created.key), "openai/gpt-4.1");
+  assert.equal(allowed.rejection, null, "non-quota key still uses normal models freely");
+});
+
 test("quota-only key whose allowedQuotas references a non-existent pool is rejected 403 QUOTA_ONLY (fail-closed)", async () => {
   // Create an API key bound to a pool ID that does not exist in the DB (dangling reference)
   const created = await apiKeysDb.createApiKey("Dangling Quota Key", "machine-b4-dangling");