American Express (Amex) is building a system that lets AI agents shop and pay on behalf of users — but right now it’s only within its own payment network, and still involves a black box that could hinder trust and auditability. Amex already participates in agentic commerce protocol projects, especially Google’s Agent Pay Protocol (AP2), which focuses on interoperability. Amex’s Agentic Commerce Experiences (ACE) developer kit, on the other hand, touches on something most protocols currently lack: Full transaction control in the payment layer.  But it still isn't completely transparent in how it handles validation. ACE uses a closed-loop system — serving as both the card issuer and the payme...