Cluster X-ray scaling relations, calibrated without cosmology, show the inferred H₀ varying by about 9 percent across the sky at roughly 4σ (Migkas et al. 2021). The direction is stable across samples and relations, and aligns with bulk-flow excesses seen independently. ΛCDM must explain it as a 900 km/s coherent flow beyond 500 Mpc, which its velocity field forbids, or as systematics that keep surviving cross-checks.
FLRW isotropy makes H₀ one number for the whole sky; nothing in the model can produce a directional expansion-rate variation of any amplitude on half-Gpc scales. Faced with one, the model can only convert it into peculiar velocities too large for its own structure formation, so it has nowhere physical to put the signal.
SCT replaces the hot-dense-center with a superluminal collision, and the constant Λ with the dynamical ratio Λ_eff(x,t) = C × Λ_parent(x,t) / λ_local(x,t) (P17). Expansion then varies with environment: sightlines through underdense regions sample enhanced Λ_eff and read a faster H₀, overdense sightlines read slower (P19). SCT quantifies exactly the observed amplitude: the predicted systematic difference between void-dominated and overdensity-dominated directions is about 9 percent, fixed by the same physics that sets the Hubble tension itself, with the variation declining toward higher redshift.
The directional coherence follows from the structure, not from motion: the KBC underdensity is not spherically symmetric around us, and the mesh hierarchy above it (P59, P60 sibling-pocket influence as secondary modulation) tilts the Λ_eff field across the sky. No 900 km/s flow is required because nothing is flowing; different directions genuinely expand at measurably different rates, and the cluster method, which reads expansion through distances rather than velocities, sees it directly. The alignment with bulk-flow directions is expected, since peculiar-velocity analyses fitting an isotropic model to an anisotropic Λ_eff field will misread the gradient as a flow.
This is the same environmental physics behind the megamaser H₀, the ladder-CMB split, and the DESI evolving dark energy artifact. There is no need to invoke impossible bulk flows or a conspiracy of X-ray systematics.
The registered kill: environment-tagged H(z) measurements in DESI finding no systematic difference between void-dominated and overdensity-dominated sightlines at the 2 percent level, after all peculiar-velocity corrections, falsifies the anisotropic-Λ_eff reading. The designed referee is eROSITA: an all-sky cluster analysis finding H₀ isotropic to better than 2 percent would simultaneously remove the observation and the mechanism's required amplitude.