The rapid proliferation of autonomous AI agents is driving a shift toward agentic commerce, where agents are expected to autonomously invoke and pay for services. While blockchain-based payments offer a programmable foundation for such interactions, the recently proposed x402 standard fails to enforce end-to-end atomicity across service execution, payment, and result delivery. In this paper, we present A402, a trust-minimized payment architecture that securely binds cryptocurrency payments to service execution. A402 introduces Atomic Service Channels (ASCs), a new channel protocol that integrates service execution into payment channels, enabling real-time, high-frequency micropayments for agentic commerce. Within each ASC, A402 employs an atomic exchange protocol based on TEE-assisted adaptor signatures, ensuring that payments are finalized if and only if the requested service is correctly executed and the corresponding result is delivered. To further ensure privacy, A402 incorporates a TEE-based Liquidity Vault that privately manages the lifecycle of ASCs and aggregates their settlements into a single on-chain transaction, revealing only aggregated balances. We implement A402 and evaluate it against x402 with integrations on both Bitcoin and Ethereum. Our results show that A402 delivers orders-of-magnitude performance and on-chain cost improvements over x402 while providing trust-minimized security guarantees.

翻译：自主AI代理的快速普及正推动代理型电商的发展，在该模式下代理需自主调用并支付服务费用。尽管基于区块链的支付为此类交互提供了可编程基础，但近期提出的x402标准未能实现服务执行、支付与结果交付的全链路原子性。本文提出A402——一种信任最小化的支付架构，可将加密货币支付安全绑定至服务执行过程。A402引入原子服务通道（ASCs），这是一种新型通道协议，将服务执行集成至支付通道中，为代理型电商提供实时高频微支付能力。在每条ASC中，A402采用基于TEE辅助适配器签名的原子交换协议，确保支付仅在请求服务被正确执行且对应结果交付后最终完成。为进一步保障隐私，A402设计基于TEE的流动性金库，该金库可私有管理ASC生命周期，并将其结算聚合为单笔链上交易，仅暴露聚合余额。我们实现了A402系统，并在比特币和以太坊上针对x402进行集成测试。实验结果表明，A402在性能和链上成本方面较x402提升数个数量级，同时提供信任最小化的安全保障。