Glossary
Clear, citable definitions of x402, agentic commerce, and the open agentic stack, the language of how AI agents discover and pay for what they need.
- ACP (Agentic Commerce Protocol)ACP, or the Agentic Commerce Protocol, is an open standard from OpenAI and Stripe that lets a buyer's AI agent complete purchases from a business inside a chat experience. It powers Instant Checkout in ChatGPT, while the business stays the merchant of record and keeps control of its catalog and fulfillment.
- Agentic CommerceAgentic commerce is commerce carried out by AI agents acting on a person or business's behalf. Instead of a human clicking buy, an agent discovers options, makes a decision, and pays, often programmatically and per use. It spans agents buying data, APIs, compute, and goods without a human completing each transaction.
- MPP (Machine Payments Protocol)MPP, or the Machine Payments Protocol, is a protocol that lets software agents pay servers for API access on a per-request basis, with no human accounts or subscriptions. Like x402, it gives machines a native way to transact. Merit Systems' MPPScan indexes the MPP ecosystem, tracking its servers, agents, transactions, and volume.
- Open Agentic CommerceOpen agentic commerce is agentic commerce built on open, permissionless protocols rather than a single company's closed platform. Any agent can discover and pay any service, and any developer can offer one, with no gatekeeper. Merit Systems uses the term for the open alternative to walled-garden checkouts like in-chat purchases.
- UCP (Universal Commerce Protocol)UCP, or the Universal Commerce Protocol, is an open standard led by Google with retailers like Shopify, Etsy, Target, and Walmart that lets AI agents discover products, build carts, and check out across many merchants without a custom integration for each. It covers the full shopping lifecycle and carries cryptographic proof of user consent.
- x402x402 is an open payment protocol that lets software, including AI agents, pay for APIs and digital services over HTTP using stablecoins, with no accounts, API keys, or manual signups. It revives the dormant HTTP 402 "Payment Required" status code so a server can request payment and a client can settle it programmatically inside a single request.