AI agents do not hold their own cards. They pay through delegated instruments that prove a human authorized the spend and constrain what the agent can do with it. As of September 2026, three protocol families cover most of the ground: Google's AP2 uses cryptographically signed mandates, the OpenAI and Stripe Agentic Commerce Protocol uses scoped shared payment tokens, and x402 settles machine-to-machine payments in stablecoins over plain HTTP.
AP2, the Agent Payments Protocol, is Google's answer to the authorization question. The user signs an intent mandate describing what the agent may buy and within what limits, and the agent later produces a cart mandate for the specific purchase. Both are verifiable credentials, so every payment carries a cryptographic chain back to a human instruction. That chain is the point: when a dispute arrives, there is evidence of what was authorized. AP2 launched in September 2025 with more than 60 partners and is deliberately payment-method agnostic, covering cards, bank transfers, and stablecoins.
The Agentic Commerce Protocol takes a narrower, more production-minded path. It powers Instant Checkout in ChatGPT, first with Etsy sellers and then Shopify merchants. The buyer's card stays vaulted with the agent platform, and the merchant receives a shared payment token scoped to that single merchant and cart amount. The merchant remains the merchant of record and runs the charge through its existing processor, so the agent never touches raw card credentials and the merchant's back office barely changes.
x402 solves a different problem: machines paying machines. Built by Coinbase in May 2025, it revives the dormant HTTP 402 "Payment Required" status code. An agent requests a resource, the server replies with a price, the agent signs a stablecoin payment and retries, and the resource comes back. Settlement takes about two seconds and fees run below a cent, which makes it suited to per-call API pricing and micropayments too small for card rails to carry.
The three are not really competitors. ACP owns the consumer checkout, AP2 owns the authorization trail across payment methods, and x402 owns the machine-to-machine long tail. What none of them fully answers yet is liability: when a mandated, tokenized, cryptographically clean payment still goes wrong, the rules for who eats the loss are being written dispute by dispute.
Go deeper: what agentic payments actually are and my live x402 tracker.