diff --git a/app/api/routes_apikeys.py b/app/api/routes_apikeys.py
index 38cdb60..ae239b5 100644
--- a/app/api/routes_apikeys.py
+++ b/app/api/routes_apikeys.py
@@ -10,7 +10,7 @@
 from app.db.session import get_db
 from app.rbac import get_current_user, require_org_permission_or_platform_admin
 from app.schemas.apikeys import ApiKeyCreate, ApiKeyCreated, ApiKeyExchangeIn, ApiKeyExchangeOut, ApiKeyOut, ApiKeyRename
-from app.services import apikey_service, org_service
+from app.services import apikey_service, billing_client, org_service
 
 router = APIRouter(prefix="/orgs/{org_id}/api-keys", tags=["api-keys"])
 exchange_router = APIRouter(prefix="/auth/api-keys", tags=["api-keys"])
@@ -234,6 +234,17 @@ def create_my_api_key(
     active = _own_keys(db, membership).filter(ApiKey.status == "active").count()
     if active >= MAX_ACTIVE_KEYS_PER_USER:
         raise HTTPException(409, f"At most {MAX_ACTIVE_KEYS_PER_USER} active keys; revoke one first")
+    # M17 (design audit gap #9): auto-enrollment (billing-service's own
+    # get_subscription_summary) means a brand-new organization's first
+    # call here still succeeds -- this only actually blocks an
+    # organization whose subscription has gone to "suspended" (mid
+    # payment-failure grace period) or "cancelled". Fails open on a
+    # billing-service outage (see billing_client's own docstring).
+    if not billing_client.organization_has_active_plan(membership.organization_id):
+        raise HTTPException(
+            402, "Your organization has no active billing plan. "
+                 "Resolve any payment issue, or reactivate a plan, before creating new API keys.",
+        )
     public_scopes = body.scopes or DEFAULT_SELF_SERVICE_SCOPES
     unknown_scopes = set(public_scopes) - set(PUBLIC_SCOPE_TO_PERMISSION)
     if unknown_scopes:
diff --git a/app/core/config.py b/app/core/config.py
index fbcc921..486c66a 100644
--- a/app/core/config.py
+++ b/app/core/config.py
@@ -347,6 +347,15 @@ class Settings:
     # why, and the concurrent-login race-safety discussion there.
     SESSION_MAX_CONCURRENT = int(os.getenv("SESSION_MAX_CONCURRENT", 5))
 
+    # M17 (design audit gap #9's remaining bullet: self-service API-key
+    # creation gated on an active billing plan). omnibioai-billing's own
+    # GET /organizations/{id}/subscription already accepts any validly-
+    # signed platform JWT whose org_id claim matches -- same shared
+    # signing key both services already trust -- so this needs no new
+    # shared secret, just the URL to call. See
+    # app/services/billing_client.py.
+    BILLING_SERVICE_URL = os.getenv("BILLING_SERVICE_URL", "http://billing-service:8005")
+
     @property
     def DATABASE_URL(self):
         return (
diff --git a/app/services/billing_client.py b/app/services/billing_client.py
new file mode 100644
index 0000000..bc103f4
--- /dev/null
+++ b/app/services/billing_client.py
@@ -0,0 +1,71 @@
+"""M17 (design audit gap #9's remaining bullet): self-service API-key
+creation should require the organization to have an active billing
+plan. The gate itself lives in routes_apikeys.py; this module is the
+one cross-service call it needs -- omnibioai-billing owns subscription
+state, omnibioai-auth doesn't duplicate it.
+
+Calls omnibioai-billing's existing GET /organizations/{id}/subscription
+(no new billing-service endpoint, no new shared secret): that route
+already accepts any validly-signed platform JWT whose org_id claim
+matches the organization being queried (see omnibioai-billing's
+app/core/iam.py::get_authorized_organization_id) -- the same signing
+key this service already uses for every real session token. A
+synthetic, minimal, single-use token is minted here (via the same
+create_access_token every login already calls) purely to satisfy that
+check; it is used for this one outbound call and never stored, logged,
+or returned to any caller.
+
+Auto-enrollment means this call itself creates a Free-plan subscription
+for an organization that has never had one at all (see
+omnibioai-billing's auto_enrollment_service.py, invoked inside
+get_subscription_summary) -- so a brand-new organization's very first
+self-service key creation still succeeds; the gate only ever actually
+blocks an organization whose subscription has gone to "suspended"
+(mid payment-failure grace period) or "cancelled".
+"""
+import httpx
+
+from app.core.config import settings
+from app.core.jwt import create_access_token
+
+_ACTIVE_STATUSES = {"active", "trial"}
+
+
+def organization_has_active_plan(organization_id: int) -> bool:
+    """Fails OPEN (True) on any billing-service error (timeout,
+    connection refused, non-2xx, malformed response) -- an outage in a
+    service this one doesn't own must never block self-service key
+    creation. This is an availability-vs-business-gate tradeoff
+    deliberately decided the same direction every other cross-service
+    check in this project's wider system has gone (quota/rate-limit
+    checks all fail open too); it is not a billing-critical path the
+    way an actual metered usage event is.
+    """
+    token = create_access_token({
+        "sub": "system:billing-plan-check",
+        "email": "",
+        "roles": [],
+        "permissions": [],
+        "org_id": organization_id,
+        "org_role": [],
+        "auth_method": "service",
+    })
+    try:
+        resp = httpx.get(
+            f"{settings.BILLING_SERVICE_URL}/organizations/{organization_id}/subscription",
+            headers={"Authorization": f"Bearer {token}"},
+            timeout=3,
+        )
+    except httpx.HTTPError:
+        return True
+    if resp.status_code == 404:
+        # NoActiveSubscriptionError -- auto-enrollment should make this
+        # unreachable in practice (see module docstring), but if it ever
+        # happens, "no subscription at all" is not an active plan.
+        return False
+    if resp.status_code != 200:
+        return True
+    try:
+        return resp.json().get("status") in _ACTIVE_STATUSES
+    except ValueError:
+        return True
diff --git a/tests/test_billing_client.py b/tests/test_billing_client.py
new file mode 100644
index 0000000..b2cfa53
--- /dev/null
+++ b/tests/test_billing_client.py
@@ -0,0 +1,84 @@
+"""app/services/billing_client.py: the one cross-service call behind
+design audit gap #9's "self-service key creation gated on an active
+billing plan." Mocks httpx.get directly -- no real omnibioai-billing
+call is ever made in this suite.
+
+Developer: Manish Kumar <manish@omnibioai.org>
+"""
+from unittest.mock import MagicMock, patch
+
+from app.services import billing_client
+
+
+def _response(status_code, json_body=None, raises_on_json=False):
+    resp = MagicMock()
+    resp.status_code = status_code
+    if raises_on_json:
+        resp.json.side_effect = ValueError("not json")
+    else:
+        resp.json.return_value = json_body or {}
+    return resp
+
+
+def test_active_status_is_true():
+    with patch.object(billing_client.httpx, "get", return_value=_response(200, {"status": "active"})):
+        assert billing_client.organization_has_active_plan(42) is True
+
+
+def test_trial_status_is_true():
+    with patch.object(billing_client.httpx, "get", return_value=_response(200, {"status": "trial"})):
+        assert billing_client.organization_has_active_plan(42) is True
+
+
+def test_suspended_status_is_false():
+    with patch.object(billing_client.httpx, "get", return_value=_response(200, {"status": "suspended"})):
+        assert billing_client.organization_has_active_plan(42) is False
+
+
+def test_cancelled_status_is_false():
+    with patch.object(billing_client.httpx, "get", return_value=_response(200, {"status": "cancelled"})):
+        assert billing_client.organization_has_active_plan(42) is False
+
+
+def test_404_no_subscription_at_all_is_false():
+    """NoActiveSubscriptionError -- auto-enrollment should make this
+    unreachable in practice, but a genuine "nothing at all" state is
+    correctly not an active plan."""
+    with patch.object(billing_client.httpx, "get", return_value=_response(404)):
+        assert billing_client.organization_has_active_plan(42) is False
+
+
+def test_network_error_fails_open():
+    import httpx
+
+    with patch.object(billing_client.httpx, "get", side_effect=httpx.ConnectError("refused")):
+        assert billing_client.organization_has_active_plan(42) is True
+
+
+def test_5xx_from_billing_service_fails_open():
+    with patch.object(billing_client.httpx, "get", return_value=_response(500)):
+        assert billing_client.organization_has_active_plan(42) is True
+
+
+def test_malformed_json_response_fails_open():
+    with patch.object(billing_client.httpx, "get", return_value=_response(200, raises_on_json=True)):
+        assert billing_client.organization_has_active_plan(42) is True
+
+
+def test_sends_a_token_scoped_to_the_requested_organization():
+    from app.core.jwt import decode_token
+
+    captured = {}
+
+    def fake_get(url, headers=None, timeout=None):
+        captured["url"] = url
+        captured["token"] = headers["Authorization"].removeprefix("Bearer ")
+        return _response(200, {"status": "active"})
+
+    with patch.object(billing_client.httpx, "get", side_effect=fake_get):
+        billing_client.organization_has_active_plan(99)
+
+    assert captured["url"].endswith("/organizations/99/subscription")
+    claims = decode_token(captured["token"])
+    assert claims["org_id"] == 99
+    assert claims["type"] == "access"
diff --git a/tests/test_me_api_keys.py b/tests/test_me_api_keys.py
index 0930a9e..590ecf0 100644
--- a/tests/test_me_api_keys.py
+++ b/tests/test_me_api_keys.py
@@ -10,6 +10,7 @@
 """
 import uuid
 from datetime import datetime, timedelta
+from unittest.mock import patch
 
 import pytest
 from sqlalchemy import create_engine
@@ -57,6 +58,22 @@ def scientist(client):
     return {"org_id": org["id"], "headers": _hdr(_login(client, email)), "email": email}
 
 
+# ── M17: self-service creation gated on an active billing plan (gap #9) ────
+
+
+def test_create_is_blocked_when_the_organization_has_no_active_plan(client, scientist):
+    with patch.object(routes_apikeys.billing_client, "organization_has_active_plan", return_value=False):
+        resp = client.post("/me/api-keys", json={"name": "notebook"}, headers=scientist["headers"])
+    assert resp.status_code == 402
+
+
+def test_create_succeeds_when_the_organization_has_an_active_plan(client, scientist):
+    with patch.object(routes_apikeys.billing_client, "organization_has_active_plan", return_value=True) as check:
+        resp = client.post("/me/api-keys", json={"name": "notebook"}, headers=scientist["headers"])
+    assert resp.status_code == 201
+    check.assert_called_once_with(scientist["org_id"])
+
+
 def test_create_defaults_to_literature_read_and_lists_own_keys(client, scientist):
     resp = client.post("/me/api-keys", json={"name": "notebook"}, headers=scientist["headers"])
     assert resp.status_code == 201