Standard sirens measure distance from first principles, and GW170817 delivered H₀ = 70 (+12/-8): independent, elegant, and toothless, straddling both camps. No second golden event has arrived, dark sirens creep toward 68-to-70 with wide errors, and the percent-level tiebreaker remains a next-decade deliverable, while both camps wait to claim its verdict.
The siren program is framed as measuring one number: whatever H₀ the events return is the universe's. The framing assumes expansion cannot depend on where the sirens are, so the method's most distinctive capability, mapping H₀ versus distance and sightline, is treated as noise reduction rather than as the measurement.
SCT registers what the single-number framing cannot: sirens are the instrument that will eventually image the Λ_eff structure directly. Counterpart events inside the KBC volume sample the locally enhanced expansion and should read near 73, agreeing with the ladder they share a neighborhood with; events beyond a few hundred megaparsecs sample progressively more of the global rate and should drift toward 67-to-70; and the full prediction is a radial profile with environmental scatter (P17, P19), the same enhancement geometry confirmed piecewise by the megamasers (73.9, local) and the CMB (67.4, global). GW170817's 70, measured at 40 Mpc with wide errors, is consistent with the profile's inner region; the discriminating data are the populations coming with A+ and Einstein Telescope sensitivity.
The framework adds a quieter layer: hereditary time (P10) contributes small frame-dependent corrections to siren redshifts exactly as it does to supernovae, so cluster-hosted and field-hosted sirens should show the same 0.5-to-1 percent environmental offsets registered for the Pantheon+ sector, testable as counterpart catalogs grow. Sirens do not break the tie between the camps; they dissolve the premise that there was one number to tie over. Foundations in Paper 1 (P17, P19) with the frame-tree treatment of Paper 2, From Chaos To Common Ancestry.
The economy holds: no new machinery, only the standing Λ_eff field read by the one probe whose distances cannot be argued with.
The registered kill is the flat profile: a future siren population (dozens of counterpart events spanning 40 Mpc to a gigaparsec) measuring H₀ constant with distance and environment at the 2 percent level, no radial drift from 73 toward 67, no environmental scatter beyond errors, would falsify the Λ_eff gradient at its most unforgiving test. SCT requires the gradient; a single global number from the cleanest distances in physics would end the environmental reading everywhere.