diff --git a/connection.capnp b/connection.capnp
index bdc3e2f..58f9084 100644
--- a/connection.capnp
+++ b/connection.capnp
@@ -43,4 +43,7 @@ struct Session {
     machineSystem @0 : MachineSystem;
     userSystem @1 : UserSystem;
     permissionSystem @2 : PermissionSystem;
+
+    vendor @3 :AnyPointer;
+    # Vendor-specific APIs outside the normal API stability
 }