Cross-Input Signature Aggregation (CISA) has been on Bitcoin’s radar for years, but with small elliptic curve signatures the tradeoffs rarely justified a soft fork. Post-quantum signatures change the calculus. Tadge Dryja makes the case for a CISA variant that can work with any signature scheme, including post-quantum, to reduce the footprint of larger PQ signatures without increasing block size. A practical look at how signature aggregation could make a post-quantum path more efficient for Bitcoin’s future. Recorded live at TABConf 7, 2025.