How does x402 compare to ACP, AP2, and UCP?

Four protocols get named together, and the honest answer is they're mostly different layers, not competitors. x402 is the payment rail itself — HTTP-native, per-request, stablecoin settlement; the natural fit when a service charges per call, which is why the API and infrastructure world adopted it. ACP, from Stripe and OpenAI, is the merchant checkout layer — it's what lets an agent buy from a store inside ChatGPT, and it's spreading through Stripe's enterprise base. UCP is Google and Shopify's take on the full shopping journey, discovery through fulfillment. AP2 is Google's agent-payments framework, and notably it uses x402 as its default stablecoin rail — which tells you these stack rather than fight. A production agent in 2026 plausibly touches two or three of them: UCP to find the product, ACP to check out at a merchant, x402 to pay an API. If the thing being bought is a metered digital resource — an API call, a dataset, compute, hashrate — x402 is the layer that fits. If it's a cart at a store, that's ACP's territory. Genuine uncertainty remains about where standards consolidate; anyone claiming certainty is selling something.