Google's Universal Cart hands baskets to stores in one direction

How quickly does a store's cart endpoint have to respond?

Google enforces no formal service level objectives for the POST /carts endpoint, but strongly recommends responding “ideally in under one second.” Slower responses don't make the transfer fail, though Google says higher latency can degrade the user experience. It also tells merchants to plan capacity for the referral traffic they expect during peak campaigns, and to throttle excess requests with standard HTTP 429 responses.

Which listings show the Buy now button for UCP checkout?

Only product listings that use the native_commerce(checkout_eligibility) product attribute, according to Google's developer guide to the Merchant Center hub. Google says the checkout feature enabled by UCP is available for select merchants; to participate in its early access program, merchants submit the interest form and complete the required technical implementation.

Does Universal Cart buy things on its own?

Google doesn't describe it that way. Its launch post splits Google's commerce work into “unlocking agentic capabilities that act on your behalf” and “designing practical tools that give shoppers confidence and control,” and says the cart “is built for that second track.” The post presents checkout as a step the shopper takes “when you’re ready to buy.”