Blockstream has submitted a Bitcoin Improvement Proposal outlining upgrade recommendations for its post-quantum signature scheme, SHRINCS. The scheme has completed production-environment testing on Blockstream’s Liquid sidechain and has a minimum signature size of 548 bytes, roughly nine times larger than Bitcoin’s current 64-byte Schnorr signatures, but significantly smaller than NIST-approved alternatives such as SPHINCS+. Blockstream’s research said Bitcoin throughput could remain near 3 transactions per second if SHRINCS is adopted, close to current levels. By contrast, adopting a NIST-approved post-quantum scheme could reduce throughput to 0.36 to 0.5 TPS. The proposal also said SHRINCS is still at an early stage, has not yet completed a security proof, and introduces additional challenges including state management and key incompatibility. Blockstream is also studying zero-knowledge proof aggregated signatures, which could potentially raise throughput to 6.7 TPS.