AP2 vs x402 vs ACP: The Agent Payment Stack Explained
AP2 (Google), x402 (Coinbase), and ACP (OpenAI and Stripe) get pitched as rivals, which is the wrong frame. They sit at different layers of the agent payment stack: AP2 proves the user authorized the purchase, ACP runs the checkout inside a chat surface, and x402 settles the payment, usually in stablecoins over HTTP. A single transaction can use all three. The tell: Google built x402 support directly into AP2, because these compose rather than compete.
Open any thread about agent payments and you will find people arguing about which protocol "wins," AP2, x402, or ACP. It is the wrong argument. Asking whether x402 beats AP2 is like asking whether the plumbing beats the light switch. They do different jobs in the same house.
Here is the frame that actually makes sense of it.
Three layers, not three rivals
An agent buying something has to answer three separate questions, and each protocol answers one:
- Was this allowed? Did the user actually authorize this agent to spend, and can you prove it later? That is authorization.
- How does the buy happen? How does the agent and the merchant agree on the cart and complete the purchase inside the chat? That is checkout.
- How does the money move? What rail actually transfers the value? That is settlement.
Map the three protocols onto those layers and the confusion evaporates.
AP2: the authorization layer
AP2, Google's Agent Payments Protocol, announced in September 2025, is a trust framework, not a payment rail. Its job is to prove, cryptographically, that a payment reflects real user intent. It does this with signed mandates:
- An Intent Mandate captures what the user allowed in advance ("buy these tickets when they drop, under this price"), which is what makes safe human-not-present purchases possible.
- A Cart Mandate is a signed, tamper-proof record of the exact items and price at checkout. What you signed is what you pay.
- A Payment Mandate is shared with the payment network to authorize a specific instrument.
Together they answer authorization, authenticity, and accountability: who allowed this, does it reflect true intent, and who is liable. AP2 is payment-agnostic, and it has backing from 60-plus companies including Mastercard, PayPal, and American Express.
ACP: the checkout layer
ACP, the Agentic Commerce Protocol from OpenAI and Stripe, announced in September 2025, standardizes the checkout between an agent and a merchant. It is what powers Instant Checkout in ChatGPT: a shopper buys inside the chat, but the checkout state and payment run on the merchant's own systems, so the merchant keeps their existing processor. The clever piece is the Shared Payment Token, a Stripe primitive scoped to a specific merchant and cart total, so ChatGPT can trigger payment without ever seeing the buyer's card. It launched with Etsy sellers, with a large wave of Shopify merchants next.
x402: the settlement layer
x402, created by Coinbase, takes the HTTP 402 Payment Required status code, reserved and unused for roughly 35 years, and makes it real. A server can respond "pay me to continue," and the agent settles in stablecoins inside the same HTTP exchange. It is a machine-to-machine settlement rail, ideal for agents paying per API call or paying each other. Coinbase has said it is moving x402 toward neutral, Linux Foundation governance. We covered its mechanics in depth in agentic payments and x402.
The decision, by use case
| You are... | Reach for | Why |
|---|---|---|
| A merchant who wants to sell inside ChatGPT | ACP | Fastest path to the ChatGPT buyer, keep your processor |
| Building delegated or human-not-present buying, or need auditable proof of authorization | AP2 | Signed mandates give verifiable intent and liability |
| Building agents that pay per request, pay each other, or settle in stablecoins | x402 | Machine-native settlement over HTTP |
| Building a full autonomous crypto payment flow | AP2 + x402 | AP2 authorizes, x402 settles, via the A2A x402 extension |
The honest part: the micropayment dream has not arrived
Since we are being accurate rather than promotional, here is the counter-narrative worth knowing. The pitch for agent payments was armies of agents paying fractions of a cent for API calls. So far, the data says otherwise. On x402, according to Chainalysis, transactions of a dollar or more grew to about 95 percent of volume through early 2026, while the ten-cent-to-a-dollar band collapsed from roughly 46 percent to 4 percent. The rail works. The tiny-payment behavior it was built for is, for now, mostly aspirational. Anyone selling you "agents will pay per token everywhere by next quarter" is ahead of the evidence.
The real signal: Google shipped x402 inside AP2
If you want proof these are layers rather than rivals, look at what Google actually built. Alongside AP2, Google shipped an A2A x402 extension, together with Coinbase, the Ethereum Foundation, and MetaMask, that lets AP2's authorization layer settle through x402. The company behind one protocol wired a supposed rival in as its own crypto settlement path. That is not what competitors do to each other. The industry is stratifying into authorize, check out, settle, not consolidating into one winner.
Where we fit
Agent commerce is exactly what we build 1ly for, and the reason we work across all three layers rather than betting on one: a real agentic purchase often needs authorization, a checkout surface, and a settlement rail, and which ones depend on whether you are selling to humans in a chat or wiring agents to pay each other. If you are building agentic payments, the first job is not picking a protocol. It is knowing which layer your problem lives in. You can see our take live at 1ly.store, or book a call.
References
- Google, Announcing the Agent Payments Protocol (AP2): the mandate model and partners.
- AP2 and x402: how AP2's authorization layer settles through x402.
- Stripe, Instant Checkout with OpenAI (ACP): how checkout runs inside ChatGPT.
- Chainalysis, x402 agentic payments adoption: the transaction-size data behind the micropayment caveat.
Frequently asked questions
No, and treating them as rivals is the most common mistake. They occupy different layers. AP2 is an authorization and trust framework, ACP is a checkout standard for buying inside an AI chat, and x402 is a settlement rail for machine-to-machine payments in stablecoins. Google even built an x402 extension into AP2, so AP2 authorizes and x402 settles.
AP2, the Agent Payments Protocol from Google announced in September 2025, is an open framework that cryptographically proves an agent was authorized to pay. It uses signed mandates: an Intent Mandate for what the user allowed, a Cart Mandate for the exact items and price, and a Payment Mandate shared with the payment network. It is payment-agnostic and works with cards, bank, or crypto.
x402, created by Coinbase, activates the long-unused HTTP 402 Payment Required status code so a server can charge an agent for a request and settle in stablecoins inside the HTTP exchange. It is moving toward neutral, Linux Foundation governance. It is a settlement rail for machine-to-machine payments, not an authorization framework.
ACP, the Agentic Commerce Protocol from OpenAI and Stripe announced in September 2025, standardizes checkout between an AI agent and a merchant. It powers Instant Checkout in ChatGPT, letting a shopper buy inside the chat while the merchant keeps their own payment processor, using a scoped Shared Payment Token instead of exposing card details.
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