In one sentence: agentic commerce rests on four layers, and each major protocol sits on one of them. MCP and A2A handle communication, UCP and ACP handle the merchant journey, AP2 handles payment authorization, and x402 and MPP handle machine-to-machine settlement. Thinking in layers avoids the common mistake of pitting them against each other when they actually stack.
The four layers of agentic commerce
When an agent buys for a human, several distinct problems have to be solved: how the agent talks to systems, how it discovers and negotiates a merchant offer, how it proves it is allowed to pay, and how money actually moves. No single protocol covers all four. That is why a real agentic purchase often chains several standards together.
- Communication layer: how an agent accesses tools and data, and talks to other agents. Standards: MCP (Model Context Protocol, Anthropic) and A2A (Agent2Agent, Google).
- Commerce layer: how an agent discovers a catalog, builds a cart, and triggers a purchase at a merchant. Standards: UCP (Google) and ACP (OpenAI/Stripe).
- Authorization layer: how you prove a human actually mandated the agent to spend, within agreed limits. Standard: AP2 (Agent Payments Protocol, Google).
- Settlement layer: how value moves between machines, often as micropayments. Standards: x402 (Coinbase) and MPP (Machine Payments Protocol, Stripe/Tempo).
Protocol comparison table
| Protocol | Backed by | Appeared | Layer | Primary role |
|---|---|---|---|---|
| UCP (Universal Commerce Protocol) | Google + Shopify, Etsy, Wayfair, Target, Walmart | Jan. 2026 | Commerce | Standardize the full merchant journey, from discovery to order management |
| ACP (Agentic Commerce Protocol) | OpenAI + Stripe | 2025 | Commerce | Agent-triggered checkout, powers ChatGPT Instant Checkout |
| AP2 (Agent Payments Protocol) | 2025 | Authorization | Prove and trace the payment mandate a human gives an agent | |
| x402 | Coinbase | 2025 | Settlement | Machine-to-machine payments via the HTTP 402 code, often in stablecoins |
| MPP (Machine Payments Protocol) | Stripe / Tempo | 2025 | Settlement | Programmable settlement between agents and services |
| MCP (Model Context Protocol) | Anthropic | 2024 | Communication | Connect a model to tools, data and actions |
| A2A (Agent2Agent) | 2025 | Communication | Let heterogeneous agents talk to each other |
UCP: Google's merchant standard
The Universal Commerce Protocol launched on January 11, 2026, announced by Google at the NRF show, co-developed with Shopify, Etsy, Wayfair, Target and Walmart, and endorsed by more than twenty players (Adyen, American Express, Best Buy, Flipkart, Macy's, Mastercard, Stripe, The Home Depot, Visa, Zalando). It is an open-source standard, published at ucp.dev.
Its promise is to remove the N x N integration bottleneck, where each merchant had to build a bespoke connection for every agent surface. UCP standardizes the full lifecycle, from discovery to order management, around capabilities (checkout, product discovery, identity linking, order management) that an agent discovers dynamically through a manifest exposed at /.well-known/ucp. Its payment architecture separates the instrument (what the consumer pays with) from the payment handler (the processor), and every authorization is backed by cryptographic proof of user consent. UCP is compatible with AP2, A2A and MCP, and supports multiple transports: the same checkout capability can be exposed over REST or over MCP. Google shipped the first reference implementation, which powers direct purchase from AI Mode in Search and the Gemini app, with the merchant remaining seller of record.
ACP: OpenAI and Stripe's agentic checkout
The Agentic Commerce Protocol, backed by OpenAI and Stripe, standardizes the moment an agent triggers a purchase at a merchant. It is what underpins Instant Checkout in ChatGPT, letting a user buy a product without leaving the conversation. It sits on the same layer as UCP (the merchant journey), which is why the two genuinely overlap on checkout while the other layers stay distinct.
AP2: proving the payment mandate
Google's Agent Payments Protocol does not move money: it answers the trust question that blocks everything else. How does a merchant or a bank know that an agent paying is genuinely acting on the orders of an identifiable human, within agreed limits? AP2 formalizes that mandate in a verifiable way, compatible with A2A and MCP. UCP itself relies on AP2 for agentic payment security.
x402 and MPP: settlement between machines
Beneath the commerce layer, value still has to move. x402, from Coinbase, revives the HTTP 402 (Payment Required) status code so an agent can pay for a resource or service directly, often in stablecoins, with no human in the loop. The Machine Payments Protocol (MPP), associated with Stripe and Tempo, targets a similar goal of programmable settlement. These protocols aim at micropayments between agents and digital services rather than at consumer-product checkout.
MCP and A2A: the communication layer
Before commerce even enters the picture, an agent needs to access tools and data, and sometimes coordinate other agents. Anthropic's Model Context Protocol standardizes connecting a model to tools and data sources. Google's Agent2Agent standardizes dialogue between heterogeneous agents. Both UCP and AP2 reuse these transports rather than inventing new ones, which neatly illustrates the stacking logic.
Competing or complementary?
The most common framing, UCP versus ACP, is partly real (both touch checkout) but largely overstated. Stripe co-founds UCP and backs ACP with OpenAI: the stated bet is coexistence, not substitution. Everywhere else, the protocols add up. A credible scenario: an agent uses MCP to read a catalog, UCP to build and confirm the cart at the merchant, AP2 to prove the user's mandate, and a payment rail (Google Pay, a PSP, or even x402 for a digital service) to settle.
Which one matters for your store?
If you sell products to consumers, what matters first is being buyable on agent surfaces: expose a clean, structured catalog, and prepare UCP integration (through your platform or Merchant Center) along with compatibility with OpenAI's agentic checkout. The payment layer (AP2, provider) is usually handled for you. The x402 and MPP layers mostly concern API and digital-service providers billed per use by other agents.
Frequently asked questions
What is the difference between UCP, ACP and AP2?
UCP standardizes the full merchant journey, ACP standardizes agentic checkout (and powers ChatGPT), AP2 proves the payment authorization a human gives. Different layers, designed to coexist.
Are these protocols competing?
Mostly complementary. The only genuine overlap is UCP and ACP on checkout. Everything else stacks.
Which protocol should an e-commerce merchant prioritize?
Exposure through UCP and ACP, since they make your catalog buyable from AI Mode, Gemini and ChatGPT. Payment is usually handled upstream by the platform.
What is x402?
A Coinbase protocol that revives HTTP 402 for direct machine-to-machine settlement, often in stablecoins, aimed at micropayments rather than physical products.
Sources
- Google, "New tech and tools for retailers to succeed in an agentic shopping era" (January 11, 2026)
- Google Developers, "Under the Hood: Universal Commerce Protocol (UCP)" (January 11, 2026)
- Google Cloud, "Announcing Agent Payments Protocol (AP2)"
- Crossmint, "Agentic payments protocols compared (MPP, ACP, AP2, x402)"
- Openfort, "MPP, x402, ACP & AP2 compared"