Nature Communications, Published online: 12 September 2026; doi:10.1038/s41467-026-77279-5 Distinguishing amorphous ice phases like low-density (LDA) and high-density (HDA) primarily relies on global or long-range structural descriptors, leaving the microscopic basis of their differences unclear. This study achieved a data-driven, probabilistic framework that identifies local hydrogen density within the first coordination shell as the key structural feature distinguishing LDA and HDA.