In ACP, the agent platform vaults the card and hands the merchant a token capped at the checkout total. In AP2, a Credential Provider keeps the card and the user signs an SD-JWT that says what the agent may do with it. In x402 there is no card and nothing to vault: the payer's wallet signs a one-off USDC transfer and a facilitator puts it on-chain.
Those are three different answers to the question of who holds the money. Most pages ranking for "AP2 vs ACP vs x402" skip that and describe layers. Several, one earlier piece of mine among them, still explain AP2 with Intent and Cart Mandates, which the v0.2 spec replaced in April 2026.
What Is the Difference Between AP2, ACP and x402?
They standardise different things. ACP is a merchant checkout API. AP2 is a format for signed evidence that a user authorised an agent. x402 is an HTTP handshake for paying on a stablecoin rail. You can use all three in one flow, and the specs increasingly expect you to.
| AP2 | ACP | x402 | |
|---|---|---|---|
| Governed by | FIDO Alliance (donated by Google, 28 Apr 2026) | OpenAI and Stripe | x402 Foundation, Linux Foundation (operational 14 Jul 2026) |
| Current version | v0.2 | 2026-04-17 |
Spec v2 |
| What it defines | Mandates and receipts | Checkout sessions, delegated payment, product feeds | 402 challenge, payment payload, facilitator API |
| Who holds the credential | Credential Provider | Agent platform's PSP or vault | Payer's own wallet |
| Proof of authorisation | User-signed SD-JWT mandate | Single-use token with an allowance
|
EIP-3009 signature per payment |
| Money moves on | Any rail the processor supports | The merchant's existing card processor | On-chain, e.g. USDC on Base (eip155:8453) |
| Dispute path | Evidence only, resolution out of scope | Normal chargeback via merchant of record | None in the spec |
| Transport | Extension to A2A, MCP and UCP | REST, plus MCP from 2026-04-17
|
HTTP headers, A2A, MCP |
The x402 Foundation launched with 40 members, including Adyen, American Express, Google, Mastercard, Shopify, Stripe and Visa. That membership overlaps almost entirely with AP2's and ACP's backers, which tells you nobody expects one protocol to win outright.
How Does ACP Checkout Work in 2026?
The merchant implements five endpoints:
Read the full article on tomcn.uk →
About the Author
I'm Tom Wang, an AI Developer & Fintech Developer — building AI agents, crypto payment infrastructure, and cross-border payout systems with Rust, Go, and TypeScript. Based in London, UK.
Currently open to new opportunities in fintech, crypto payments, and AI agent engineering.
