The publication of the telomere-to-telomere CHM13 sequence (Nurk et al., 2022) and the first draft Human Pangenome Reference (Liao et al., 2023) jointly mark the end of the linear single-reference paradigm that has governed human genomics for two decades. GRCh38 omits roughly 200 megabases of repetitive and acrocentric sequence and carries a documented European-ancestry bias; the new resources close most of that gap and reframe the reference itself as a structured graph over 47 phased haplotypes spanning multiple ancestry groups. This article addresses a question that the celebratory tone of the original announcements largely sidestepped: how mature is the actual transition? We propose the Pangenome Adoption-Readiness Transition Index (PARTI), a normalized composite metric on [0,1] that aggregates five dimensions of practical readiness — reference completeness gain (D_comp), population and ancestry representation (D_pop), toolchain native-graph support (D_tool), clinical-pipeline integration (D_clin), and variant-call equivalence relative to legacy reference workflows (D_eq) — into a single comparable score via geometric mean. PARTI is applied to five canonical use-cases: germline short-variant calling, structural-variant detection, repeat-rich and segmental-duplication analysis, pharmacogenomic interpretation, and clinical diagnostic pipelines for rare disease and oncology. Resulting scores range from 0.62 (structural-variant detection, the largest immediate win) down to 0.21 (clinical diagnostic pipelines, the slowest mover). The analysis identifies clinical-pipeline integration (D_clin) as the binding constraint across four of five use-cases: graphnative variant callers exist, but the regulatory, interpretive, and infrastructure layers — variant databases, ACMG/AMP guideline operationalization on a graph reference, electronic-healthrecord liftover, and laboratory information-management-system compatibility — remain calibrated to GRCh38. PARTI thus reframes the transition as a stratified engineering and policy problem rather than an undifferentiated paradigm shift, and identifies the specific subsystems on which the practical end of the single-reference paradigm is contingent.