Agentic commerce protocols explained: UCP, ACP, AP2, MCP and the Personal Agent Protocol

They are shared rules for the conversation between an AI agent acting for a person and a business selling something. A person might ask an agent to find a present, compare prices or reorder something. To do that safely, the agent and the business have to agree on a few things:

• Where to start: how the agent finds out what a business supports.
• Who is asking: which agent this is, and which person it acts for.
• What is for sale: products, prices, carts and checkout.
• What the person agreed to: a record of the approval that the store, the payment provider and the card network can all check.
• How to pay: a payment credential the agent can use without seeing the card number.

No single standard covers all of this. The Linux Foundation's Agentic AI Foundation said so directly in a post titled "There Is No One Agentic Commerce Protocol" on October 6, 2026 (AAIF blog, read October 29, 2026). Each protocol below handles one or a few of these jobs.

Underneath everything is a transport, the way agents call each other and call services. Above it sit seven layers. As of October 29, 2026 (sources in the sections below):

Some protocols cover several layers. UCP spans discovery through checkout and plugs into payment and authorization. PAP spans discovery, identity and sign-in, and touches authorization through its Operations extension. AP2 sits at the authorization layer. Machine-to-machine payment standards such as x402 and MPP sit off to the side, because they are designed mainly for agents paying per request for APIs, data and compute.

The Personal Agent Protocol, nicknamed "Poppy", is a draft standard from Meta and Sierra for how a person's own AI agent signs in to a business and acts within permissions the person granted. Sierra introduced it on October 6, 2026, published a v0.1 draft on October 9, and v0.2 followed on October 24. Draft 0.3 is current, and 0.1 and 0.2 are frozen (Sierra, Sierra: sharing a draft, PAP overview, read October 29, 2026).

How it works (PAP 0.3 spec, read October 29, 2026):

• Discovery. A business publishes /.well-known/poppy.json.
• Agent identity. The agent's client ID is an HTTPS URL that serves OAuth client metadata, including its public keys. The agent proves its identity with a signed token.
• Sessions. The agent starts signed out, as a guest, carrying a Poppy-Session header. It then signs the person in through OAuth. One session can span the business's website, its APIs (including MCP) and the business's own agent.
• Scopes. Each business defines its own permission scopes; PAP defines none. Optional hints mark scopes as reversible, irreversible or touching personal data.

Operations approvals. The Operations extension asks for "approval tied to exact terms and no duplicate execution" (PAP Operations, read October 29, 2026):

• When an action needs the person's say-so, the business refuses with approval_required and returns an operation ID, a revision, a human-readable summary, optional machine-readable terms and an expiry.
• The agent asks the person, then retries with the approval (a Poppy-Approval header over HTTP, or a field in the MCP call).
• Any change to the terms creates a new revision, so an approval covers only the terms the person saw.
• The business must carry out each operation at most once.
• The approval is not signed by the person; the spec lists user-signed approvals as an open topic.

Status, as of October 29, 2026:

• It is a draft. The spec and docs are Apache-2.0 on GitHub (read October 29, 2026); no neutral foundation is named yet.
• There is no payments extension. Sierra lists payments without sharing card details as possible future work.
• Meta and Sierra have not announced production deployments. The PAP site lists community-built demos, which it says are not reviewed or endorsed by the authors; one, Print with Poppy, is a live photo-printing store where the person approves the exact order through Operations and then pays on a separate checkout (PAP demos, read October 29, 2026).
• Sierra's launch partners include Genesys, Instinct, Rocket, Stripe and Walmart. On October 9, 2026 Sierra added 35 design partners, including Adyen, Cloudflare, Mastercard, OpenAI, PayPal, Plaid, Target, Visa and Wells Fargo (Sierra, read October 29, 2026).
• Sierra describes PAP as complementary to UCP: UCP covers shopping, while PAP covers identity and permission for any kind of task.

PACT. On the same day, October 6, 2026, Decagon announced PACT (Personal Agent Consent & Trust), developed with Instinct. It solves a similar problem on top of A2A: the person approves scopes through an OAuth device flow, and the agent carries a short-lived delegation token. Its spec is labelled 1.0 and has no payment or purchase-approval flow. Decagon said it is joining the Personal Agent Protocol working group "to help shape an industry standard" (Decagon, PACT spec, read October 29, 2026).

The Universal Commerce Protocol (UCP) is an open standard that lets AI agents and stores find products, build carts and check out. Stores publish a profile at /.well-known/ucp, agents publish one of their own, and the two use the capabilities both support. It runs over REST, JSON-RPC, MCP and A2A, and includes identity linking with OAuth 2.0 and an optional AP2 extension for payment mandates (ucp.dev, read October 29, 2026).

• Versions are dated. The latest release is 2026-08-25, which added payment schedules (deposits, instalments), split payments, network-token credentials and delegated identity providers (UCP releases, read October 29, 2026).
• Governance sits with member companies through a Governing Council, a Tech Council and domain councils for food, lodging and payments (UCP announcements, read October 29, 2026). The UCP site also lists endorsers including Visa, Mastercard, American Express, PayPal, Adyen and Klarna, and shows a draft lodging spec, with food "coming soon".
• In use: Google's Universal Cart is rolling out in the US from October 15, 2026, across Search and the Gemini app, with checkout powered by UCP (Google, read October 29, 2026).

For how profiles, capabilities and transports work, see What is UCP?. Gratos supports UCP.

The Agentic Commerce Protocol (ACP) comes from OpenAI and Stripe, its founding maintainers. It is Apache-2.0, and its initial stable release is dated September 29, 2025. Its README still says it is "currently in beta", and its latest stable release, 2026-04-17, added cart, feeds, orders, authentication and an MCP binding. The README says the project intends to move to neutral foundation stewardship (ACP on GitHub, read October 29, 2026).

ChatGPT Instant Checkout used ACP. On March 24, 2026 OpenAI said the initial version of Instant Checkout "did not offer the level of flexibility" it wanted. Merchants now use their own checkout, and those who want a deeper integration build ChatGPT apps. At the same time OpenAI extended ACP to product discovery, naming Target, Sephora, Nordstrom, Lowe's, Best Buy, Home Depot and Wayfair as integrated for discovery (OpenAI, read October 29, 2026).

So ACP has not gone away: it is now mainly how product data reaches ChatGPT, and its checkout spec is still published. Visa's Intelligent Commerce Connect lists ACP among the protocols it accepts, alongside UCP (Visa, April 8, 2026, read October 29, 2026).

The Agent Payments Protocol (AP2) is a standard for proving what a person authorized an agent to buy. Google created it, and on April 28, 2026 donated it to the FIDO Alliance along with version 0.2, which added "Human Not Present" payments (Google, AP2, read October 29, 2026).

A mandate is a signed record of what the person approved. AP2 v0.2 has two kinds (AP2, read October 29, 2026):

• Checkout Mandate: shared with the merchant.
• Payment Mandate: shared with the credential provider, the card network and the processor.

Each can be:

• Closed: bound to one finalized checkout or one exact amount. In direct mode, the person approves a closed checkout.
• Open: a set of constraints the person approves in advance, such as a limit, a merchant or a time window. In Human Not Present mode, the agent later completes a purchase on its own, inside those limits.

AP2's samples cover card payments and x402. Google's donation post speaks of "growing support" but names no production deployment.

FIDO's role. FIDO announced its agentic work on April 28, 2026 through two groups: its Payments Technical Working Group, chaired by members from Visa and Mastercard, building on contributions of AP2 and Mastercard's Verifiable Intent; and a newly formed Agentic Authentication Technical Working Group, chaired by members from CVS Health, Google and OpenAI, focused on "how users securely and privately delegate actions to AI agents while maintaining strong, phishing-resistant authentication" (FIDO Alliance, read October 29, 2026).

Mastercard Verifiable Intent is Mastercard's format for the same idea, a verifiable record of what the person asked the agent to do. It was co-developed with Google and contributed to FIDO on April 28, 2026 (Mastercard, FIDO Alliance, read October 29, 2026).

They are the transport layer, and most commerce protocols run over them rather than competing with them.

• MCP (Model Context Protocol) lets an AI model call tools and read data from a service. Its current specification revision is dated 2026-07-28 (MCP blog, read October 29, 2026). The MCP Registry, a public list of MCP servers, is "currently in preview" and warns that breaking changes or data resets may occur (MCP Registry, read October 29, 2026). UCP, ACP's 2026-04-17 release and PAP all name MCP as a transport.
• A2A (Agent2Agent) lets agents talk to other agents, with each agent describing itself in an Agent Card. AP2 is available as an A2A extension (AP2), UCP lists A2A as a transport (UCP core concepts), and PACT builds on A2A 1.0 (PACT spec), all read October 29, 2026.

The Agentic AI Foundation (AAIF) is a foundation hosted by the Linux Foundation, announced on December 9, 2025 with MCP, goose and AGENTS.md as its founding projects (Linux Foundation, read October 29, 2026). A2A joined as a Growth Stage project in August 2026 (A2A blog, August 27, 2026, read October 29, 2026), and AAIF lists 10 projects (AAIF projects, read October 29, 2026). AAIF does not host UCP, ACP, AP2 or PAP.

A store wants to know which agent is calling and who stands behind it. Most approaches converge on one technique: the agent signs its HTTP requests (HTTP Message Signatures, RFC 9421) with a key the store can look up.

• Web Bot Auth is that approach for automated traffic. The IETF webbotauth working group has adopted one document, draft-ietf-webbotauth-httpsig-protocol, at version -01, dated October 29, 2026. It is a draft, not yet an RFC (IETF Datatracker, read October 29, 2026). Agents publish their keys at /.well-known/http-message-signatures-directory (Cloudflare docs, read October 29, 2026).
• Cloudflare signed agents, introduced August 28, 2025, is a bot classification, an extension of Cloudflare's verified-bots program, for agents directed by an end user that sign their requests with Web Bot Auth. The initial cohort was ChatGPT agent, Goose, Browserbase and Anchor Browser (Cloudflare, read October 29, 2026).
• Visa Trusted Agent Protocol (TAP), launched October 14, 2025 and developed with Cloudflare, uses agent-specific HTTP Message Signatures that Visa describes as aligned with Web Bot Auth. A signature is bound to the merchant's domain and the operation, and can carry agent intent, consumer recognition and optional payment information (Visa, GitHub, read October 29, 2026).
• Mastercard said on September 30, 2026 that it is working with Skyfire, a Know Your Agent (KYA) provider, and with Cloudflare on web and payment-network signals, and that it is testing in the US "a probability score indicating the likelihood that a transaction was initiated by an AI agent" (Mastercard, read October 29, 2026).
• PAP takes a different route: the agent identifies itself through OAuth client metadata rather than Web Bot Auth.

Know Your Agent (KYA) is fragmented. It is a goal, not one standard. Visa announced an Agentic Directory of agents and merchants it has verified (June 10, 2026, Visa, read October 29, 2026); Mastercard works with Skyfire; and EMVCo says it "may consider" KYA as a next step (EMVCo, read October 29, 2026). A Visa, Mastercard and Ant International collaboration on KYA interoperability was reported by The Asian Banker in September 2026 (read October 29, 2026); no spec has been published. At the W3C, the Agent Identity Registry Protocol Community Group launched on April 24, 2026 (W3C, read October 29, 2026); community groups are not W3C Working Groups (W3C Community Groups, read October 29, 2026).

The networks give agents a payment credential that is not the card number: a token tied to the agent, the merchant or the amount, plus a way to check that the person approved. As each describes it:

• Visa Intelligent Commerce is Visa's program for agent payments. On April 8, 2026 Visa announced Intelligent Commerce Connect, one integration that accepts TAP, MPP, ACP and UCP and handles Visa and non-Visa cards. It is a pilot, with Aldar, AWS, Diddo, Highnote, Mesh, Payabli and Sumvin (Visa, read October 29, 2026). On June 10, 2026 Visa announced an Agent Score, an Agentic Directory of agents and merchants it has verified, and a collaboration with OpenAI; the release gives no launch date (Visa, read October 29, 2026).
• Mastercard Agent Pay is Mastercard's program for agent payments, paired with Verifiable Intent (see AP2 above). In June 2026 Mastercard announced Agent Pay for Machines for agents paying other services, with early adopters including Adyen, Cloudflare, Coinbase, Stripe and Tempo (Mastercard, read October 29, 2026). Its AI-agent probability score is in testing in the US (September 30, 2026, Mastercard, read October 29, 2026).
• American Express announced an ACE (Agentic Commerce Experiences) developer kit and Agent Purchase Protection for purchases by registered agents on April 14, 2026, as reported by Digital Commerce 360 (read October 29, 2026). On October 13, 2026 TechCrunch reported (read October 29, 2026) an Amex Intent Intelligence Framework, in which an authenticated intent yields a "Proof of Intent" token that is exchanged for a payment credential.
• Link wallets for agents, which Stripe announced on April 29, 2026, let a person enable an agent to pay with Link: "a one-time-use card is issued per task, and you approve each payment" (Stripe, read October 29, 2026). Stripe said on September 8, 2026 that Meta's Muse uses it, and that "the consumer approves the transaction total in the chat interface for every purchase" (Stripe, read October 29, 2026).

EMVCo, the card industry's technical body, published "EMV Agentic Payments – Framework for Specifications" as a v1.0 draft for comment on September 1, 2026; the comment period closed September 30. It describes Intent Services, a shared way to register, reference and retrieve the intent a consumer authorized. It is a framework, not yet a specification (EMVCo, read October 29, 2026).

A separate group of standards lets an agent pay per request for data, compute or an API call. These are mainly not consumer checkout: they usually have no cart and no shipping.

• x402 uses the HTTP 402 "Payment Required" status so a server can ask for payment and the agent can pay inline. It is now run by the x402 Foundation under the Linux Foundation, operational since July 14, 2026 (Linux Foundation, read October 29, 2026). AP2's samples include x402.
• MPP (Machine Payments Protocol), co-authored by Stripe and Tempo, was announced in March 2026 (Visa, March 18, 2026, read October 29, 2026) and expanded at Stripe Sessions (Stripe, read October 29, 2026). Visa has published a card specification and SDK so agents can pay by card inside MPP, and Visa Intelligent Commerce Connect accepts it.
• Mastercard Agent Pay for Machines (June 2026) covers the same ground on the card network (see above).

As of October 29, 2026:

The Agentic Payments Alliance is not a standards body. It was launched by Rain, a stablecoin payments company, on August 18, 2026, and describes its work as research, testing and policy advocacy (Rain, read October 29, 2026). It has not published protocol specifications.

Status as of October 29, 2026, from the sources cited above:

This applies to any agent that buys gifts for people.

Exact totals versus approved limits. The standards offer two ways to get a person's approval:

• Approve the exact total. The person sees the final price, with tax and shipping, and approves that amount. This is an AP2 closed mandate, or a PAP Operations approval tied to one revision of the terms. If anything changes, the person approves again.
• Approve a limit in advance. The person sets constraints, such as "up to $50, from these stores, by this date", and the agent completes the purchase later without asking again. This is an AP2 open mandate in Human Not Present mode.

Gifts make the choice harder than ordinary shopping. The recipient's address may not be known when the gift is picked, and shipping and tax depend on it, so the total can change after the person looks at it. Under exact-total approval that means a second approval; under a limit, the agent can finish if the new total fits. Exact-total approval is the stronger promise to the person paying, and a limit is smoother. The two consumer wallets cited above use per-purchase approval: Stripe's Link wallets for agents ask for approval of each payment, and Stripe says Muse users approve the total for every purchase.

Why a person's approval matters. A gift is money spent on someone else's behalf, often sent to a third person who never asked for it. An approval record answers the questions that come up afterwards: did the payer agree to this item at this price, did the agent stay within what was agreed, and can the store, the payment provider and the card network all check that. AP2 mandates and Verifiable Intent are designed so each party can check that answer. PAP's revisions tie an approval to exact terms, though the PAP spec notes an approval does not itself prove the person saw them. The at-most-once rule in PAP Operations means one approval cannot be carried out twice.

For what agentic gifting is and who offers it, see What is agentic gifting?.