x402 vs MPP, AP2, ACP and L402: agent payment protocols compared

x402 vs MPP, AP2, ACP and L402: agent payment protocols compared

Of the agent payment protocols published since 2025, only three compete head-on: x402, Stripe and Tempo's Machine Payments Protocol (MPP), and Lightning Labs' L402. All three let a single HTTP request carry its own payment. The others answer different questions: Google's AP2 proves a person authorized an agent's purchase, the OpenAI and Stripe Agentic Commerce Protocol (ACP) handles checkout through an assistant, and the Visa and Mastercard programs authenticate the agent and tokenize the card. News coverage often presents them as a race. Read closely, most of them divide the problem between them.

This comparison is the fifth chapter of the Group's book *The x402 Economy*, rewritten as a standalone reference. It is current to 27 September 2026.

What is the Agentic Commerce Protocol (ACP)?

OpenAI and Stripe released ACP on 29 September 2025 under the Apache 2.0 license, alongside a feature that let ChatGPT users in the United States buy from Etsy sellers without leaving the chat. ACP is about checkout: a person shopping through an AI assistant. The assistant collects the buyer's choice of product and payment method, hands the merchant a narrowly scoped payment token, and the merchant charges that token through its usual payment processor. The merchant remains the seller of record, with its own refund and support obligations. Card payments, disputes and consumer protections work as they do for any online purchase.

ACP assumes a person is present and choosing. It is not designed for a program paying a few cents for a data lookup in the middle of a task.

What is the Agent Payments Protocol (AP2)?

Google published AP2 on 16 September 2025 with more than 60 partners, among them Adyen, American Express, Mastercard, PayPal, Coinbase and Worldpay. AP2 is about authorization. Its central object is the mandate, a signed record of what a person told an agent it may buy: for example, "buy this jacket in size M when the price drops below $120". The merchant and the payment network can check the mandate and know a real person approved this purchase within these limits.

AP2 does not move money itself. It works with cards, bank transfers and stablecoins, and Google and Coinbase published an extension that uses x402 as the stablecoin rail beneath AP2's mandates. AP2 exists largely to produce evidence for a dispute that the law has not answered: who bears the loss when an agent buys something its owner did not want.

What is the Machine Payments Protocol (MPP)?

Stripe and Tempo, a blockchain for payments that Stripe backed, published MPP on 18 March 2026. Like x402, MPP lets any web address answer a request with a payment demand. It supports two kinds of payment: stablecoins on the Tempo network, and cards and buy-now-pay-later through Stripe's "Shared Payment Tokens", which let an agent use a person's card without seeing the card number.

MPP is the closest thing x402 has to a direct competitor. It solves the same problem, a request carrying its own payment, with a different network and with cards included. Stripe also accepts x402 (secondary reports date that to February 2026), so a seller using Stripe can offer both. Stripe's stated reason for building a protocol: "Making a purchase today can require an agent to create an account, navigate a pricing page, choose between subscription tiers, enter payment details, and set up billing—steps that often require human intervention."

What is L402?

L402 is the oldest protocol here. Lightning Labs first published it in 2020 under the name LSAT and later renamed it (specification). It uses the same 402 status as x402, with Bitcoin's Lightning Network in place of stablecoins:

1. The server answers with a Lightning invoice and a credential called a macaroon.
2. The client pays the invoice and gets back a secret, the preimage, as proof.
3. It retries with the macaroon and the preimage together.

The server can check them without looking anything up. L402's strengths are the Lightning Network's speed and Bitcoin's independence from any single issuer. Its weaknesses, for many sellers, are that it prices in Bitcoin rather than dollars and that Lightning payments need the payer to have a funded channel. The two protocols are close enough in design that some tools support both.

What are Visa's Trusted Agent Protocol and Mastercard's Agent Pay?

Visa and Mastercard have each built programs for agents that pay with cards. Visa calls its protocol the Trusted Agent Protocol; Mastercard calls its program Agent Pay. Both do two things. They authenticate the agent, so a merchant can tell a registered AI platform from an unknown bot. And they tokenize the card, so the agent carries a limited stand-in rather than the card number.

These programs do not create a new way to move money; the money still moves over card networks. They answer a trust question: is this agent who it says it is, and is it allowed to use this card? Both networks are also premier members of the x402 Foundation.

How do the agent payment protocols compare?

Sorted by the question each one answers, they stop looking like rivals:

And in more detail:

A single purchase can use several at once. An agent might hold an AP2 mandate from its person, meet an x402 price at a data service, and pay in USDC on Base. A shopping assistant might use ACP to check out and a card network's agent program to prove who it is.

Where do x402, MPP and L402 actually compete?

On the second row, "how does a request carry its payment", x402, MPP and L402 compete directly. On the fourth, stablecoins compete with cards. Card payments bring chargebacks, fraud protection and universal acceptance. Stablecoin payments bring low fixed costs, settlement in seconds and no account. For a ten-dollar purchase by a person, cards usually win. For a one-cent purchase by a program, stablecoins usually do.

That suggests a plausible division of labor: cards, with agent tokens and mandates, for larger purchases a person approves; stablecoin rails such as x402 for small, frequent purchases a program makes on its own. The second category is the one the web never managed to serve, and the one HTTP's 402 status code was reserved for. Whether it grows is the question of how big the x402 market actually is.

Which protocol should a seller or buyer choose?

• If you sell small, frequent operations to programs, x402 has the broadest backing and tooling (a neutral foundation, Stripe and Cloudflare support, a reference implementation under Apache 2.0). If you use Stripe, you may be able to offer MPP as well.
• If your buyers are people shopping through an assistant, look at ACP and your existing card processor.
• If you need proof that a person approved an agent's purchase, look at AP2 mandates, which can sit above x402.
• If your buyers hold Bitcoin on Lightning, L402 is the native choice.
• Whatever you choose, measure calls per payer. Early payers are often the seller and its friends. A protocol can be sound while the market is small; see what we learned selling on x402.

The Group's market uses x402 with USDC on Base: see The 130-offer x402 market, explained. For the basics, start with What is x402? and for the governance of the winner of the standards contest so far, Who built x402 and who governs it.

What are the primary sources?

Stripe and OpenAI on ACP (29 September 2025); Google Cloud on AP2 (16 September 2025); Stripe on MPP (18 March 2026); Lightning Labs' L402; the x402 version 2 specification. The descriptions of Visa's and Mastercard's programs are summarized from the Group's research notes.