PISA demo shows how Payjoin and CISA could shrink Bitcoin transactions

A prototype unveiled at Plan ₿ Week in Lugano pairs Payjoin privacy with cross-input signature aggregation to cut fees on collaborative payments Privacy on Bitcoin has always come with a surcharge. A new prototype called PISA is trying to lower the bill. Developers demonstrated PISA on October 23, 2026, during the Plan ₿ Week and Forum events in Lugano, Switzerland. The project combines Payjoin with Cross-Input Signature Aggregation, better known as CISA, to make collaborative Bitcoin transactions smaller and cheaper. Start with the two ingredients.