x402 vs AP2 vs ACP vs MPP vs UCP: which should your agent use?

Last reviewed: August 2026

Two jobs, five names

Most confusion about agent payment protocols comes from comparing all five as if they compete. They split cleanly by job. x402 and MPP move money between machines over HTTP: an agent pays a server per request, no account, no checkout page. ACP and UCP are checkout pipes: they let an AI surface (ChatGPT for ACP, Google Search, AI Mode, Gemini, and YouTube for UCP) complete a purchase against a merchant’s existing systems. AP2 is neither; it is an authorization layer proving what the human allowed the agent to buy, and it can ride along with the others. Sort a product question into one of those two jobs and the protocol usually picks itself.

The one-table version

x402: HTTP requests that pay for themselves

x402 revives HTTP status code 402 ("Payment Required"). A client calls an endpoint; the server answers 402 with a machine-readable challenge naming the price, asset, network, and recipient; the client signs a stablecoin payment and replays the request with a payment header; the server verifies, settles, and serves the response. No account, no API key negotiation, no checkout page. That shape is why it fits agents: every step is a plain HTTP exchange a program can complete alone.

Its honest limitations: payments are stablecoin-only, so somebody has to hold USDC; there is no built-in dispute or refund protocol (the endpoint you pay defines its own semantics); and it says nothing about proving your human authorized the purchase. For pay-per-call commerce those gaps rarely matter. For buying a sofa, they do.

MPP: the newer machine-to-machine rail

MPP (Machine Payments Protocol) is the closest thing to a direct x402 competitor on this page: the same request, pay, replay loop for agents buying API access per call, co-authored by Stripe and Tempo and launched in March 2026 with the Tempo mainnet. Stripe’s distribution makes it credible, and if your stack is already committed to Tempo it is the native choice.

The honest differences, stated from x402’s side of the fence (we operate x402 endpoints, so weigh the bias): x402 is about a year older, settles on multiple chains rather than one, moved to neutral Linux Foundation governance in July 2026, and has the larger set of live paid endpoints and client libraries today. MPP is single-ecosystem and months old. Notably, Stripe backs both: it settles x402 payments on Base and co-authored MPP, which reads as the rail question staying open rather than settled. If MPP wins meaningful adoption, expect the two to converge or bridge; the challenge-and-replay shape is nearly identical.

AP2: proving the human said yes

AP2 (Agent Payments Protocol) attacks a different problem: when an agent buys on a human’s behalf, who is accountable? Its answer is mandates: verifiable, signed credentials capturing what the user authorized (an intent mandate) and what was actually in the cart (a cart mandate). Processors and issuers can then treat an agent purchase as provably authorized rather than as fraud-shaped traffic. AP2 is rail-agnostic, covering cards and bank transfers, and crypto through an x402 extension, which is the clearest sign these protocols compose rather than compete.

Its honest limitations: it is an authorization framework, not a settlement mechanism, so it needs rails and ecosystem adoption to do anything, and adoption is the current gap. The coalition is wide, production deployments are still thin. Of the five protocols here it is the one you are least likely to need directly in 2026; it matters most as the accountability layer the checkout protocols can adopt.

ACP: checkout inside ChatGPT

ACP (Agentic Commerce Protocol) is the most product-shaped of the five: it defines how an AI surface like ChatGPT completes a purchase against a merchant’s systems, passing a shared payment token so the merchant charges the buyer without ever seeing raw card details, and the merchant remains merchant of record. If you sell goods and want distribution inside ChatGPT, ACP is that pipe, and there is no crypto anywhere in it.

Its honest limitations: it serves the assistant-to-merchant path, not agent-to-API payments; the assistant platform decides which merchants participate; and your agent does not "choose" ACP so much as inherit it by selling through a surface that speaks it.

UCP: checkout across Google surfaces

UCP (Universal Commerce Protocol) is Google’s answer to the same checkout problem, announced in January 2026 and co-developed with Shopify, Etsy, Target, Walmart, and other large retailers. It standardizes how catalogs, carts, and checkout connect across Google Search, AI Mode, Gemini, and YouTube Shopping, with payment through Google Pay or the retailer’s own flow. For merchants it is less a choice than a distribution requirement: if Google surfaces matter to your sales, UCP is how agentic shopping reaches you there.

Its honest limitations mirror ACP’s: it is a merchant-and-surface protocol, not something an independent agent adopts, and it lives inside Google’s ecosystem. ACP and UCP competing for merchants while AP2 offers both an authorization layer is the current state of the checkout side.

The worked example: card issuance over x402

Where x402 gets interesting is when the thing being bought is itself spending power. Most of the commercial web speaks none of these five protocols; it wants a card number. Laso closes that loop over x402: an agent pays one challenge and receives a virtual prepaid card for exactly that amount, usable at any U.S. checkout.

# 1. Unpaid call returns the 402 challenge with the exact USDC price
curl "https://laso.finance/get-card?amount=50"

# 2. An x402 client pays the challenge and replays; the response includes
#    a card_id plus API credentials
# { "card": { "card_id": "card_abc123", "usd_amount": 50, "status": "pending" }, ... }

# 3. Poll the free endpoint until status is "ready" (~7-10 seconds),
#    then read card_number, expiry, and CVV
curl "https://laso.finance/get-card-data?card_id=card_abc123" \
  -H "Authorization: Bearer eyJ..."

One protocol payment in, one card out, and the agent can now transact with the entire card-accepting economy, not just the sliver of it that has adopted an agent protocol. The full walkthrough is at Issue a virtual card with one x402 call, and laso.finance/SKILL.md is the agent-readable version.

So which should your agent use?

• Your agent buys API calls, data, compute, or per-call services: x402 today; watch MPP if your stack is Tempo-based.
• Your agent shops at normal web merchants: x402 to issue a card, then ordinary checkout. No checkout protocol gets an independent agent a way to pay arbitrary merchants.
• You are a merchant wanting agentic checkout: ACP for ChatGPT, UCP for Google surfaces, realistically both as they roll out.
• You are building delegated purchasing with accountability across card rails: AP2, accepting that you are early.
• You are building a serious commerce agent for the long run: expect to speak a checkout protocol per surface, AP2 for authorization, and x402 (or eventually MPP) for machine payments. They stack.

Frequently asked questions

Are x402, AP2, ACP, MPP, and UCP competitors?

Only in pairs. x402 and MPP compete directly on machine-to-machine payments; ACP and UCP compete for merchant checkout, on different surfaces (ChatGPT vs Google). AP2 is an authorization layer that composes with the others, and it even includes an x402 extension for stablecoin settlement.

Which agent payment protocol has the most adoption in 2026?

For machine-to-machine payments, x402: v2 shipped in December 2025, Stripe settles x402 payments on Base, Cloudflare supports it, and the x402 Foundation operates under the Linux Foundation with about 40 members. For consumer checkout, ACP is live in ChatGPT and UCP is live across Google surfaces. AP2 has the broadest coalition but the earliest-stage deployment, and MPP is the newest, launched March 2026.

What is MPP and how is it different from x402?

MPP (Machine Payments Protocol) is an open standard from Stripe and Tempo, launched March 2026, for agents paying services per HTTP request. It solves the same problem as x402 with a nearly identical challenge-and-replay shape. The practical differences: x402 is older, settles on multiple chains (Base and Solana in practice), sits under neutral Linux Foundation governance, and has more live endpoints; MPP settles on the Tempo chain and its ecosystem is still forming.

What is UCP?

UCP (Universal Commerce Protocol) is Google’s open standard, announced January 2026 with Shopify, Etsy, Target, Walmart, and others, for connecting merchant catalogs, carts, and checkout to Google’s AI surfaces: Search, AI Mode, Gemini, and YouTube Shopping. It is a merchant-side protocol; an independent agent does not adopt UCP so much as encounter merchants through surfaces that speak it.

Does x402 require cryptocurrency?

Yes. x402 settles in stablecoins, USDC on Base or Solana in practice, so the paying agent needs a funded wallet or a managed wallet service that signs on its behalf. MPP is also stablecoin-based, on Tempo. AP2, ACP, and UCP work over traditional card rails.

Can an AI agent buy from a normal online store with these protocols?

Only where the store has integrated with an assistant platform (ACP or UCP). For everywhere else, the working bridge is to use x402 to issue a prepaid card for the exact total (one call on Laso), then pay the merchant like any cardholder. That works at any card-accepting checkout regardless of which protocols the merchant has heard of.

More guides

• How to give your AI agent a credit card — An AI agent cannot pass credit underwriting, but it can issue itself a virtual prepaid card over an API in about a minute. The working pattern, with real requests: x402 payment in, card number out.
• x402 vs Stripe Issuing for AI agents — Two real ways to put a card in an AI agent’s hands: Stripe Issuing behind a business account, or x402 card issuance the agent drives itself. An honest comparison of onboarding, funding, controls, and when each wins.
• Issue a virtual card with one x402 call — A complete, runnable walkthrough: pay one x402 request in USDC and receive a virtual prepaid card with number, expiry, and CVV. Real endpoints, real response shapes, error handling included.
• All agent guides, or how Laso compares to the alternatives