diff --git a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/geom.rs b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/geom.rs
index 7747112..abeb80a 100644
--- a/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/geom.rs
+++ b/crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/geom.rs
@@ -163,10 +163,12 @@ fn upload_pairs(v: &[[f64; 2]]) -> CudaSlice<f64> {
         .expect("upload pairs")
 }
 
-/// R6-2 step 2 (`RTX_E3_UB_DEVICE=1`, default off): the band's surface
-/// velocity at the foot and the end-of-rebuild imposition on the device.
+/// R6-2 step 2: the band's surface velocity at the foot and the
+/// end-of-rebuild imposition on the device — default ON since its
+/// two-period 3D gate held (2026-09-25); `RTX_E3_UB_DEVICE=0` restores the
+/// host. Bodies without a device velocity fall back to the host.
 pub(crate) fn ub_device_enabled() -> bool {
-    std::env::var("RTX_E3_UB_DEVICE").is_ok_and(|v| v == "1")
+    !std::env::var("RTX_E3_UB_DEVICE").is_ok_and(|v| v == "0")
 }
 
 /// R6-2 step 2: the body's surface velocity in the device's form at one