This paper presents the first observational prediction derived from the Six-Field Ontology, a resonance-based framework proposing an emergent origin for particles, forces, and spacetime. Building on the now complete architectural foundation—including the substrate operator H^sub\hat{H}_{sub}H^sub—the analysis shows that the cosmological constant Λ cannot remain strictly constant over cosmic time. Instead, Λ must exhibit a small, smooth, and monotonic evolution as a direct consequence of the changing resonance state of the underlying substrate. The prediction defines a clear empirical signature, fully within the measurement capabilities of current and upcoming cosmological observatories. As such, it provides a concrete criterion by which the Six-Field Ontology can be supported or falsified. With this step, the Six-Field program transitions from a conceptual unification framework to a scientific theory in the strict sense, concluding the initial portfolio of methodological, mathematical, and structural papers with a testable and externally verifiable consequence.