UCP vs ACP: Comparing Agentic Commerce Protocols

Two Protocols, One Problem

The race to define how AI agents transact online has produced two serious contenders: the Universal Commerce Protocol (UCP), co-developed by Shopify and Google (with endorsers including Visa, Best Buy, Target, and Walmart), and the Agent Commerce Protocol (ACP), created by Amazon. Both protocols aim to solve the same fundamental problem, giving AI agents a structured way to discover products and complete purchases, but they approach it with starkly different philosophies.

This comparison is based on the current public specifications of both protocols as of early 2026. Both are evolving rapidly, and the landscape may shift significantly. Treat the details here as a snapshot, not a permanent assessment.

Design Philosophy

UCP takes a federalist approach. The protocol treats merchants as sovereign participants. Each merchant hosts their own UCP endpoints, controls their own data, sets their own pricing, and handles their own fulfillment. UCP defines the contract between agents and merchants but doesn't insert itself as an intermediary. There's no central authority routing transactions or taking a platform fee.

ACP takes a platform-centric approach. Transactions flow through Amazon's infrastructure. Merchants list on ACP through Amazon's unified product catalog, and payments are processed through Amazon Pay. The agent interacts with Amazon's API layer, which then dispatches to individual merchants. This gives ACP the advantage of consistency, where every merchant looks the same to the agent, but it means Amazon sits in the middle of every transaction.

The philosophical divide is real and has practical consequences. UCP gives merchants more control and independence. ACP gives agents a simpler, more uniform integration experience.

Technical Comparison

Discovery

UCP defines per-merchant discovery endpoints. Each merchant exposes a /ucp/products endpoint with standardized query parameters for search, filtering, and pagination. Agents query merchants individually or use aggregator services. Product schemas are standardized, but merchants control their own catalog data.

ACP provides a single, centralized product search API. Agents query Amazon's unified catalog, which includes products from Amazon's own inventory and third-party ACP merchants. Filtering and search use Amazon's product graph, which is mature and well-indexed.

Verdict: ACP is easier to integrate for discovery because it's a single endpoint. UCP requires agents to discover and query multiple merchants, but returns data directly from the source, reducing the risk of stale pricing or inventory.

Checkout Flow

UCP uses a multi-step checkout session model. The agent creates a session, adds items, attaches identity and payment tokens, and then submits for consumer confirmation. The merchant's payment handler processes the payment independently.

ACP uses Amazon's one-click purchase infrastructure, adapted for agents. The agent submits a purchase intent, Amazon handles payment through the consumer's linked Amazon account, and the order enters Amazon's fulfillment pipeline (or the merchant's, for third-party sellers).

Verdict: ACP is faster and more streamlined for consumers who already have Amazon accounts. UCP is more flexible, supporting any payment handler and any merchant, but requires more integration work.

Authentication & Identity

UCP uses a decentralized identity model. Consumers link their identity through an identity provider (which could be their agent platform, a dedicated identity service, or even a self-hosted solution). The agent receives scoped tokens that prove the consumer's identity without exposing credentials to the merchant.

ACP uses Amazon account authentication. Consumers authorize their agent to use their Amazon account, and all transactions are tied to that Amazon identity. This is simpler but requires every consumer to have an Amazon account.

Verdict: ACP is simpler for consumers already in Amazon's ecosystem. UCP is more inclusive and doesn't lock consumers into a single platform.

Payment Handling

UCP is payment-handler agnostic. Merchants can use Stripe, Adyen, Visa Direct, PayPal, or any payment processor that implements the UCP payment token exchange specification. This means consumers can pay with any method their chosen payment handler supports.

ACP uses Amazon Pay exclusively. All transactions are processed through Amazon's payment infrastructure, using the payment methods the consumer has on file with Amazon.

Verdict: UCP offers more flexibility for both merchants and consumers. ACP is simpler but creates payment lock-in.

Ecosystem & Backing

UCP Ecosystem

Co-developers: Shopify (native platform support), Google (Shopping and AI Mode integration)
Collaborators: Etsy, Target, Walmart, Wayfair
Payment Handlers: Stripe, Adyen, Visa, Mastercard, American Express, PayPal (based on announced support)
Agents: Google Gemini / AI Mode, with broad third-party agent support
Endorsers: Best Buy, Flipkart, Macy's, The Home Depot, Visa, Zalando
Development Model: Open specification, public GitHub, reference implementations

ACP Ecosystem

Platform: Amazon (primary), with third-party sellers through Amazon Marketplace
Payment: Amazon Pay (exclusive)
Agents: Amazon Alexa+, Amazon Rufus, with API access for third-party agents
Merchants: Amazon's existing third-party seller base (millions of sellers)
Development Model: Amazon-controlled specification, SDK distributed through AWS

Reach

ACP has an immediate advantage in merchant count because every Amazon Marketplace seller is automatically ACP-enabled. UCP has stronger backing from independent merchants and platforms outside Amazon's ecosystem.

When to Choose UCP

Choose UCP if you're building an agent that needs to:

Work across multiple platforms: not just Amazon. UCP lets your agent shop on Shopify stores, Google Shopping, and independent retailers.
Support flexible payment methods: consumers want to pay with their preferred method, not just what's in their Amazon account.
Maintain merchant relationships: you're building a white-label agent for a retailer who doesn't want transactions flowing through Amazon.
Operate internationally: UCP's payment-handler flexibility makes it easier to support region-specific payment methods.
Stay vendor-neutral: you don't want your agent's commerce capabilities tied to a single company's platform.

When to Choose ACP

Choose ACP if you're building an agent that:

Prioritizes simplicity: ACP's centralized model means fewer integration points and faster time to market.
Targets Amazon's catalog: if your users primarily want to buy products available on Amazon, ACP gives direct access.
Needs fulfillment logistics: Amazon's fulfillment network (FBA) is unmatched. ACP transactions can leverage Prime shipping and Amazon's logistics.
Wants minimal payment complexity: Amazon Pay handles everything, reducing PCI scope and payment integration work.

Can You Support Both?

Yes, and many agent developers are doing exactly that. The protocols aren't mutually exclusive. An agent can use UCP for independent merchants and ACP for Amazon's catalog, routing transactions to whichever protocol the merchant supports. Some middleware libraries are emerging that abstract both protocols behind a unified interface.

The key insight is that UCP and ACP solve different parts of the market. Amazon dominates online retail in some categories and regions but is a minority player in others. A well-built shopping agent should be able to reach merchants wherever they are.

The Bigger Picture

The existence of two competing protocols is actually healthy for the ecosystem. Competition drives both specifications to improve. It also reduces the risk of a single-protocol monoculture that could be captured by one company's interests.

The most likely long-term outcome is coexistence, similar to how REST and GraphQL both thrive in the API world. UCP will likely dominate the open web and independent commerce, while ACP will dominate within Amazon's ecosystem. Smart agent developers will support both.

What matters most is that agentic commerce is happening, the protocols are shipping, and the infrastructure for AI-powered shopping is being built right now. Whether you choose UCP, ACP, or both, the important thing is to start building.

Explore UCP-Compatible Tools

If you are starting with UCP, browse 57+ UCP-enabled merchants live in the directory today. The payment handlers category lists the processors that have confirmed UCP support, including Stripe, Adyen, Visa, and PayPal. And the developer tools category has the SDKs and conformance suites you need to build compliant integrations.