x402 vs AP2 vs ACP
Short answer: x402, AP2 and ACP are not three competing versions of the same thing. They cover different layers of an AI agent payment: - x402 (Coinbase, now the x402 Foundation) settles a pay-per-request on-chain (typically stablecoin) payment over HTTP. - AP2 (Google, now at the FIDO Alliance) proves that the user authorized what the agent buys, on any rail. - ACP (OpenAI + Stripe) runs a merchant checkout inside a chat interface on card rails.
Many real systems will use more than one.
Last checked: 2026-09-28. All three protocols are changing quickly; dates and governance below are taken from each protocol's own primary sources.
Side-by-side comparison
| x402 | AP2 | ACP | |
|---|---|---|---|
| What it standardizes | Requesting and settling a payment for an HTTP resource | Proof of what the user authorized (mandates) | Agent-to-merchant checkout |
| Initiated by | Coinbase Developer Platform | OpenAI + Stripe | |
| First published | May 6, 2025 | September 16, 2025 | September 29, 2025 |
| Payment rail | On-chain tokens on Base / Solana (any ERC-20 / SPL token, e.g. USDC) | Card, real-time bank transfer, stablecoin (rail-agnostic) | Card rails via existing payment processors |
| Authorization model | Payment signed by the payer, verified and settled by a facilitator | Signed Intent Mandate + Cart Mandate (verifiable credentials) | Buyer approves checkout in the chat; processor tokenizes credentials |
| Typical use | An agent paying per API call, per data request or per piece of content | An agent buying on a user's behalf, including pre-authorized "Human Not Present" purchases | A shopper buying from a merchant without leaving the AI chat |
| Merchant of record | Not applicable (resource server is paid directly) | Depends on the underlying rail and merchant | The business selling the product |
| License | Apache-2.0 | Apache-2.0 | Apache-2.0 |
| Governance (2026) | x402 Foundation, Linux Foundation (operational launch July 14, 2026) | Donated to the FIDO Alliance (April 28, 2026) | OpenAI and Stripe as Founding Maintainers |
| Self-described adopters among 13 payment providers we audited* | 4: Circle, Coinbase, Crossmint, Stripe | 0 | 4: Stripe, Adyen, PayPal, Checkout.com |
*From the Agentic Payments Readiness Report 2026 (checked 2026-09-28). A provider counts only if its own docs or official GitHub say it supports the protocol, not if it's merely named as a launch partner. "0 for AP2" means none of the 13 self-describe an AP2 integration in their own docs yet, although 60+ companies were named as AP2 collaborators at launch.
Which one should you use?
- Your agent needs to pay for APIs, data or content per request, with no accounts or API keys: x402. A server answers with HTTP 402 and payment requirements, the agent signs a stablecoin payment, and a facilitator settles it on-chain (x402 FAQ).
- Your agent buys things for a person, and you need proof of exactly what that person approved: AP2. The Intent Mandate records the instruction and its limits, the Cart Mandate records the exact items and price, and both are signed (Google Cloud announcement).
- You are a merchant who wants to be purchasable inside ChatGPT or another AI chat: ACP. The buyer approves in the chat, and the business stays merchant of record (Stripe).
- You need card payments: AP2 or ACP. x402 settles on-chain only.
- You need stablecoins: x402 or MPP natively, or AP2 through its x402 extension.
- You sell through Google's AI surfaces (AI Mode, Gemini): look at UCP, which is Google's checkout standard.
What about MPP and UCP?
Two newer protocols often appear in the same comparisons:
- MPP (Machine Payments Protocol), published March 18, 2026, is "co-authored by Tempo and Stripe" (Stripe). The spec site describes it as "the open standard for machine-to-machine payments via HTTP 402" (mpp.dev). That puts it in the same layer as x402. Stripe says it supports "stablecoins as well as fiat with cards and buy now, pay later payment methods." It also offers "Sessions" for pay-as-you-go stablecoin payments (mpp.dev).
- UCP (Universal Commerce Protocol), announced January 11, 2026, is "an open-source standard designed to power the next generation of agentic commerce." It was developed by Google "in collaboration with industry leaders including Shopify, Etsy, Wayfair, Target, and Walmart" (Google Developers Blog). That puts it in the same layer as ACP (merchant checkout). Google says it is "compatible with Agent Payments Protocol (AP2)" and integrates via APIs, A2A and MCP.
Rough mapping: x402 and MPP = paying for a resource over HTTP 402. ACP and UCP = agent-to-merchant checkout. AP2 = proof of what the user authorized, usable underneath either.
How they fit together
- AP2 + x402. Google's AP2 announcement describes an x402 extension, co-developed with Coinbase, the Ethereum Foundation and MetaMask, for stablecoin payments inside AP2 (Google Cloud). AP2 handles the "did the user authorize this?" question; x402 moves the money.
- One provider, two protocols. In our audit, Stripe self-describes support for both x402 and ACP in its own docs (Readiness Report).
- MCP is a separate layer. The Model Context Protocol is how an agent discovers and calls tools, including payment tools; it is not a payment protocol. AP2 is built as an extension of Agent2Agent (A2A) with MCP support. See MCP payments.
What the protocols leave to you
Each protocol answers one question well: how to request and settle (x402), how to prove authorization (AP2), or how to check out (ACP). A company running many agents still has to decide, per agent: - how much it may spend, per transaction and per period; - which merchants or categories are allowed; - when a human must approve.
AP2's Intent Mandate carries the limits of one user instruction. Budgets and approval rules across a whole fleet of agents usually sit in the wallet or platform layer on top of the protocols. See AI agent spending controls.
FAQ
Is x402 a competitor to AP2? Not directly. x402 settles a payment for an HTTP resource on-chain (typically in stablecoins); AP2 proves what a user authorized and works across cards, bank transfers and stablecoins. AP2 even has an x402 extension for its stablecoin payments.
Which agent payment protocol has the most adoption? Among the 13 payment providers in our Readiness Report (checked 2026-09-28), x402 and ACP tie with four providers each that self-describe support in their own docs; none self-describes AP2 yet. That measures provider documentation, not transaction volume.
Does ACP support stablecoins? The primary sources we reviewed (Stripe's announcement and the ACP GitHub specs) describe checkout on card rails via existing processors and do not specify stablecoin support.
Can an AI agent use x402 without a Coinbase account? Yes. x402 is an open protocol: any wallet that can sign a compatible payment can be a client, and anyone can run a facilitator (x402 FAQ).
Who controls these protocols now? x402 is governed by the x402 Foundation under the Linux Foundation (operational launch July 14, 2026). AP2 was donated by Google to the FIDO Alliance (April 28, 2026). ACP is maintained by OpenAI and Stripe as Founding Maintainers.
Disclosure
This guide is published by PinkWallet, which is building Pink Agentic AI Payment (early access): an MCP server that lets AI agents pay, plus a console where companies set spending rules. We are not neutral in this space, which is why every factual claim above links to a primary source and our adoption data is open (CSV, CC BY 4.0).
