Bitcoin mainnet confirmed the first QSB transaction without modifying consensus rules or a soft fork.QSB replaces elliptic-curve security assumptions with hash-based protections designed to withstand attacks using Shor’s algorithm.Generating each QSB spend requires approximately $75–$150 in off-chain cloud GPU computation before broadcast occurs.Nonstandard QSB transactions bypass ordinary mempool relay and require direct submission to a participating miner.QSB protects legacy outputs but does not secure Taproot, Lightning channels or previously exposed keys.