The redshift drift watches expansion happen: dz/dt from the same spectral lines measured decades apart, no candles, rulers, or ladders. ΛCDM predicts its specific curve, positive at low z, negative past z of 2, at centimeters per second per decade, and ESPRESSO has opened the campaign the ELT and SKA will finish. Nothing has been measured yet; everything will be, and every framework's expansion history is on the table in advance.
The model's drift curve assumes one global H(z) along every sightline: a single function of redshift, identical toward every quasar. Environment-dependence of expansion would fracture the curve into sightline-dependent families, structure the standard forecast does not contemplate because the assumption forbids it.
SCT's registered expansion history writes directly into this observable. The Λ_eff dynamics displace H_SCT(z) from the ΛCDM curve at the sub-percent level for z below 2 (the registered departure band), growing toward higher redshift, so the SCT drift curve differs from the standard forecast in shape, most visibly in where dz/dt crosses zero and how steeply it descends, a clean pre-registered discriminant once ANDES-class precision arrives (P17, P18). The deeper signature is the fracture: sightlines through void-dominated corridors sample enhanced Λ_eff and drift differently from overdense sightlines (P19), so SCT predicts the drift, measured toward enough quasars, resolves into an environment-tagged family rather than one curve, the same gradient the H₀ methods drew, finally watched in real time.
The test's purity makes it the program's endpoint: no population systematics, no calibration chains, just the metric moving or not moving as each framework requires. The expansion structure is laid out in Paper 7, From Chaos To Cosmic Expansion, with the registered H(z) departures in Paper 10, From Chaos To Confirming Falsifiability.
No new premises: the standing five-premise expansion mechanism, awaiting the one instrument that measures its time derivative directly.
The kill is pre-registered and absolute: ELT-era drift measurements finding dz/dt matching the ΛCDM curve at the 0.1 percent level across sightlines of contrasting environment, one global curve, no fracture, no shape displacement, would falsify the Λ_eff dynamics in the most direct measurement physics permits. SCT requires both the shape departure and the environmental family; a single clean constant-Λ curve ends the framework's expansion sector.