What is the difference between UCP and ACP?
Both define how an agent places an order with a merchant, and they come from different camps. ACP was published by OpenAI and Stripe for purchases inside ChatGPT. UCP was launched by Google with Shopify, Etsy, Wayfair, Target and Walmart, for any agent and any commerce stack, starting with AI Mode and the Gemini app.
| Protocol | Owner | Launched | What it does | Who needs it | Status in October 2026 |
|---|---|---|---|---|---|
| Model Context Protocol (MCP) | Anthropic, stewarded by the Agentic AI Foundation under the Linux Foundation since 9 December 2025 | 25 November 2024 | Lets an agent discover and call a shop’s tools, such as catalogue search or stock lookup | Shops that want agents to query the catalogue directly instead of scraping pages | Supported by ChatGPT, Claude, Gemini, Microsoft Copilot and VS Code |
| Universal Commerce Protocol (UCP) | Google, co-developed with Shopify, Etsy, Wayfair, Target and Walmart | 11 January 2026 | Standard checkout an agent can complete with any merchant, over REST, MCP, AP2 or A2A | Shops whose buyers use Google AI Mode or Gemini | Checkout live for eligible US retailers first |
| Agentic Commerce Protocol (ACP) | OpenAI and Stripe, open source under Apache 2.0 | 29 September 2025 | Lets ChatGPT pass an order and a delegated payment token to the merchant, who stays merchant of record | Shops with a large ChatGPT audience | Instant Checkout moved into apps inside ChatGPT in March 2026 |
| Agent Payments Protocol (AP2) | Google, donated to the FIDO Alliance on 28 April 2026 | 16 September 2025 | Signed mandates that prove what the person authorised the agent to buy | Shops that accept payments from agents, above all recurring or unattended ones | Version 0.2 released 28 April 2026 |
| x402 | Coinbase, with an A2A x402 extension launched alongside AP2 | Extension announced 16 September 2025 | Payment per request in stablecoins over the HTTP 402 status code | APIs and data sellers charging per call | Niche for retail goods |
A2A, the Agent2Agent protocol, is the messaging layer between agents. UCP and AP2 both state compatibility with it, so a merchant rarely implements it directly.
Do I need both UCP and ACP?
Usually not at the same time. A shop needs the protocol of each channel where its buyers actually ask, so the choice follows the audience, and both protocols read the same product data underneath.
A Shopify merchant gets much of UCP from the platform. A merchant on Salesforce Commerce Cloud, SAP Commerce or a custom stack has to implement it. ACP matters if ChatGPT sends real buyers: in March 2026 an OpenAI spokesperson said Instant Checkout was moving to apps, with ACP “serving as the infrastructure that connects users to merchants” (Digital Commerce 360, 6 March 2026). Both launched in the United States, so a Swiss shop prepares the data now and the protocol when the channel opens here. We build that layer as part of agentic checkout with Autobasket Convert.
What is AP2, and what is a mandate?
AP2 is the proof layer for payments made by software. A mandate is a cryptographically signed record of what the person approved, which the merchant and the payment network can verify before money moves.
At launch Google described two mandates (Google Cloud, 16 September 2025). An intent mandate records the instruction and its limits, for example “reorder printer paper every month, up to CHF 400”. A cart mandate binds approval to one basket and one amount. More than 60 organisations backed the launch, among them Adyen, American Express, Coinbase, Etsy, Mastercard, PayPal, Revolut, Salesforce and Worldpay.
Version 0.2, released when Google donated AP2 to the FIDO Alliance on 28 April 2026, adds Human Not Present payments, where the agent completes the purchase later under a mandate signed earlier. Verifiable Intent, co-developed with Mastercard, went to FIDO at the same time. The spec is still moving, so check the current mandate names on ap2-protocol.org before you build. The office reorder use case shows a mandate check step by step.
Human Not Present payments matter most in B2B, where a buyer’s procurement agent reorders on a schedule. What a supplier has to expose for that, from contract prices to stock without a login, is set out in agentic commerce for B2B suppliers.
How is MCP different from A2A?
MCP connects an agent to tools, and A2A connects an agent to other agents. For a shop, MCP is the one that matters: a server that exposes a handful of typed tools, such as search the catalogue under a maximum price or return stock for a SKU in a postcode.
At its handover to the Agentic AI Foundation, MCP counted more than 97 million monthly SDK downloads and about 10,000 active servers (MCP blog, 9 December 2025). The merchant decides what is exposed and at what rate, and the agent no longer has to parse the product page. An MCP server does not replace structured data on the page, since assistants that search the open web still read the page.
Which protocols does a Swiss merchant actually need?
Fewer than the table suggests, and in a fixed order. First complete structured data, because every protocol reads the same product, price and stock. Then the protocol of the channel your buyers use, and AP2 checks before you accept orders placed without the customer present.
| Situation | What to build first |
|---|---|
| Customers ask Google, then buy on your site | Structured data now, UCP when AI Mode checkout opens in Switzerland |
| Large ChatGPT audience | Structured data and an OpenAI product feed, ACP through a ChatGPT app |
| B2B customers reorder under standing rules | AP2 mandate checks and an MCP server for catalogue and stock |
| Most payments run through TWINT | Check with your payment provider, since we found no TWINT support in the published protocol documents |
A protocol built for a channel that is not open in your market costs money without bringing orders. The Machine Readability Sprint does the data step, and the Switzerland guide covers TWINT and CHF.