Four protocols shape how AI agents pay, and they do different jobs. Google’s AP2 records the human’s consent, while OpenAI and Stripe’s ACP runs the checkout. x402 and MPP move the money. Visa and Mastercard are building their own agent programmes alongside them.
These are the payment pipes of the agentic economy, and the names invite confusion. AP2, the Agent Payments Protocol, is Google’s; PayPal is one partner among many. ACP, the Agentic Commerce Protocol, came from OpenAI and Stripe. A single agent purchase can touch several of them without any one company handling every stage.
The short answer
| Protocol | Who launched it | When | The job it does |
|---|---|---|---|
| x402 | Coinbase, now the x402 Foundation (Linux Foundation) | May 2025 | Pays for a resource inside a single web request, usually in stablecoins |
| AP2 (Agent Payments Protocol) | Google, with 60+ launch partners | September 2025 | Proves a human authorised the agent to spend, and how much |
| ACP (Agentic Commerce Protocol) | OpenAI and Stripe | September 2025 | Runs the checkout between an agent and a merchant |
| MPP (Machine Payments Protocol) | Stripe and Tempo | March 2026 | Bills agents over time: subscriptions, streaming usage, reconciliation |
The protocols can work together, though no purchase needs all four. An agent might hold an AP2 mandate, check out through ACP and pay on whichever rail the merchant supports. A paid API call suits x402; ongoing billing suits MPP. The mix depends on what is being bought, and from whom.
x402: the settlement primitive
x402 uses HTTP status code 402, Payment Required, so an agent can pay for access inside a single web request. There is no account and no invoice. The agent signs a stablecoin transfer, and the server verifies it and returns the resource.
Coinbase launched x402 in May 2025. The Linux Foundation announced the x402 Foundation in April 2026 and reported its operational launch in July, with 40 founding organisations. Members include Google, Stripe, Visa, Mastercard, American Express, AWS, Microsoft, Cloudflare, Shopify, Circle and the Solana Foundation.
Shan Aggarwal, Coinbase’s chief business officer, said at the foundation launch: “x402 moves us toward a more open financial system where sending value online is as simple as sending an email.”
The usage figures need handling with care. An independent analyst found that the headline counter on x402.org had shown the same figures since March 2026. Chainalysis counted more than 100 million x402 payments on Base alone. A Visa and Artemis report, using data to 21 April 2026, counted 178.3 million raw transactions worth $135.7 million since x402’s launch. Stripping out test and wash activity left roughly 109.6 million transactions and $15 million in adjusted volume. That discards about 89% of the reported dollar volume. The transactions survived the clean-up far better than the dollars did.
Best for: pay-per-call APIs, data access, one agent paying another for a resource.
AP2: the authorisation layer
AP2 records whether a human authorised the agent to spend. It does so with a chain of signed mandates. An Intent Mandate records what the user asked for, and a Cart Mandate records what the agent chose. A Payment Mandate then carries that authority to the payment rail.
Google announced AP2 in September 2025 as an extension of its Agent2Agent protocol. Its more than 60 launch partners included Mastercard, American Express, PayPal, Adyen and Coinbase, and the count passed 100 by late October 2025. AP2 is rail-agnostic: a mandate can authorise payment by card, bank transfer or stablecoin.
Stavan Parikh, Google’s vice president and general manager of payments, said agents that transact for users need a common way to authenticate them and convey their authority to spend.
The crypto link is direct. Coinbase built the x402 extension for AP2, so an AP2-authorised purchase can settle in stablecoins over x402.
Best for: any agent spending someone else’s money, where proof of consent matters as much as the payment.
ACP: the checkout layer
ACP handles the merchant checkout. OpenAI and Stripe released the Agentic Commerce Protocol in September 2025 as an Apache 2.0-licensed open standard, and it powered Instant Checkout in ChatGPT. The agent passes on the buyer’s choice and the merchant receives a narrowly scoped payment token. The merchant remains the merchant of record.
PayPal joined as a payment provider the following month. The consumer product had a rougher ride than the protocol. Only about 30 Shopify merchants had taken part by February 2026, a Forrester analyst told CNBC. In March, OpenAI ended Instant Checkout in favour of retailer apps inside ChatGPT. The protocol stayed available.
Best for: agents buying physical or retail goods from merchants who want to keep the customer relationship.
MPP: the billing layer
MPP bills agents beyond a single payment. It covers metered API use, subscriptions and streaming payments that must be started, cancelled and reconciled. Stripe and Tempo launched the Machine Payments Protocol on 18 March 2026, the day Tempo’s payments blockchain went live. A streaming payments feature followed the next month.
MPP settles through Stripe, with Tempo as its default stablecoin chain, and it also takes cards. The specification is published, and Parallel Web Systems has integrated it. Parallel’s founder, Parag Agrawal, said the company integrated machine payments with Stripe so agents could pay per API call.
Best for: recurring and usage-based agent billing, especially for businesses already on Stripe.
The card networks did not sit this out
Visa introduced its Trusted Agent Protocol in October 2025 with Cloudflare and other partners. Signed web requests help merchants tell shopping agents from bots, the identity problem behind Know Your Agent checks. Visa Intelligent Commerce adds agent-specific payment credentials.
In June 2026, Mastercard launched Agent Pay for Machines. It lets software pay across cards, bank accounts and stablecoins, with spending limits enforced by the network. Coinbase, Stripe and Adyen are among more than 30 companies involved.
Both networks also sit inside the x402 Foundation. Rubail Birwadker of Visa said: “Payments need to be as open and interoperable as the web itself for agent-driven commerce.” Each network, in other words, has a framework of its own and a seat at the open-standards table.
Which protocol fits?
No single protocol covers every job in an agent purchase, so the practical question is which stages a product needs.
- Selling data or compute to agents: x402 supports payment per request.
- Letting agents spend on a user’s behalf: AP2-style mandates can record the user’s authorisation.
- Selling goods to agent shoppers: ACP, alongside Visa and Mastercard’s agent programmes.
- Charging agents on an ongoing basis: MPP, or Stripe’s wider agentic tools.
The ownership map is lopsided. Google holds authorisation through AP2. Stripe co-authored two of the four protocols, ACP with OpenAI and MPP with Tempo, and it also sits in the x402 Foundation and Mastercard’s Agent Pay group. Coinbase originated x402, which the Linux Foundation now governs.
Demand is still the open question
The plumbing is easier to measure than the demand. Visa and Artemis’s adjusted figure of about $15 million in cumulative x402 volume counts payments; it cannot say how many were made by autonomous agents. More agents may arrive, but the adjusted figures do not yet show mass adoption.
Frequently asked questions
Is AP2 the same as ACP? No. AP2 is Google’s authorisation protocol: it proves an agent was allowed to spend. ACP, from OpenAI and Stripe, runs the checkout with a merchant.
Is x402 owned by Coinbase? Coinbase created it. Since 2026 it has been governed by the x402 Foundation under the Linux Foundation, with Google, Stripe, Visa and Mastercard among the members.
What is MPP? The Machine Payments Protocol, launched by Stripe and Tempo in March 2026, handles recurring and streaming payments for agents.
How much money actually moves over x402? Less than the headline figures suggest. A Visa and Artemis report put cumulative adjusted volume at about $15 million to 21 April 2026, once test and wash activity was removed.
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