I checked every Universal Cart merchant. None on Magento.
Google launched Universal Cart at I/O 2026 last week. An intelligent cart that follows users across Search, Gemini, YouTube, and Gmail. ALM Corp published the list of named early checkout merchants on May 20: Nike, Sephora, Target, Ulta Beauty, Walmart, Wayfair, and Shopify brands. I read that list twice looking for a Magento store. None. That's the article. Below: the five-protocol stack you'd otherwise have to read five different specs to understand, the one decision your existing payment processor has already made for you, and a thirty-day Magento-specific playbook to ship before agent-routed traffic starts flowing past your store. If your store runs on Magento or Adobe Commerce, agent-routed traffic is going to flow past you - first in the US, then Canada and Australia "in the coming months," then the UK. The agent layer isn't going to wait for Adobe Commerce to ship native UCP support. The merchants in the first cohort had thirty days of head-start. Most of that window is already gone. Here's what to ship before the rest of it closes. The five-protocol stack, compressed Four protocols define how an AI agent buys something on behalf of a user. A fifth ties payments together. UCP - the discovery layer. Your store publishes a manifest at /.well-known/ucp declaring its capabilities, transports, and payment handlers. MCP - the transport layer. Agents dispatch your commerce tool calls over MCP messages. ACP - OpenAI and Stripe's checkout protocol. Stripe-led coalition. AP2 - Google's payment-authorization protocol. Sixty-plus partners signed at launch: Adyen, American Express, Mastercard, PayPal, Coinbase, Revolut, Worldpay, and more. MPP - Stripe's machine-payments protocol. Same family as ACP. Benji Fisher's synthesis post on dev.to is the sharpest framing I've read: UCP discovers, MCP transports, ACP and AP2 authorize. Read it if you haven't. The UCP spec itself is densifying fast. A loyalty extension landed on May 19 ( #340 ). A schema-validated documentation har