UCP vs ACP: Comparing Agentic Commerce Protocols

The race to define how AI agents transact online has produced two leading contenders: the Universal Commerce Protocol (UCP) and Amazon's Agent Commerce Protocol (ACP). Both aim to give AI agents a structured way to discover products and complete purchases, but they take fundamentally different approaches.

This comparison is based on the public specifications as of early 2026. Both protocols are evolving rapidly.

#Design Philosophy

UCP takes a federated approach. 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 through Amazon's unified product catalog, and payments are processed through Amazon Pay. The agent interacts with Amazon's API layer, which dispatches to individual merchants.

The philosophical divide 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 via the /.well-known/ucp manifest. Each merchant exposes their own MCP endpoint with standardized tools for product search, checkout, and fulfillment. Agents query merchants individually or use discovery services like the UCP Registry to find stores.

ACP provides a single, centralized product search API. Agents query Amazon's unified catalog, which includes products from Amazon's inventory and third-party ACP merchants.

Verdict: ACP is easier to integrate — it's one endpoint. UCP requires discovering multiple merchants, but returns data directly from the source with live pricing and availability.

#Checkout Flow

UCP uses MCP tool calls for a multi-step checkout. The agent creates a checkout session, adds items by variant ID, attaches payment tokens, and submits for consumer confirmation. The merchant's payment handler processes the payment independently.

{
  "method": "tools/call",
  "params": {
    "name": "create_checkout",
    "arguments": {
      "items": [{ "variant_id": "gid://shopify/ProductVariant/123", "quantity": 1 }],
      "identity_token": "consumer_token"
    }
  }
}

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.

Verdict: ACP is faster for consumers with Amazon accounts. UCP is more flexible — any payment handler, any merchant, any platform.

#Authentication & Identity

UCP uses a decentralized identity model. Consumers link their identity through an identity provider. 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 identity.

Verdict: ACP is simpler for Amazon customers. UCP doesn't lock consumers into a single platform.

#Payment Handling

UCP is payment-handler agnostic. Merchants can use Stripe, Adyen, Google Pay, PayPal, or any processor that implements the UCP payment token specification. The manifest declares supported payment handlers:

{
  "payment_handlers": {
    "com.google.pay": [{ "id": "gpay", "version": "2026-01-11" }],
    "dev.shopify.card": [{ "id": "shopify.card", "version": "2026-01-15" }]
  }
}

ACP uses Amazon Pay exclusively. All transactions are processed through Amazon's payment infrastructure.

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

#Transport Layer

UCP uses the Model Context Protocol (MCP) over HTTP. Agents connect to merchant MCP endpoints using JSON-RPC 2.0, discover available tools via tools/list, and call them via tools/call. This means any MCP-compatible client can interact with UCP merchants.

ACP uses a proprietary REST API distributed through AWS SDKs.

Verdict: UCP's MCP foundation means it benefits from the broader MCP ecosystem — any MCP client library works. ACP requires Amazon-specific SDKs.

#Ecosystem & Backing

#UCP Ecosystem

• Co-developers: Shopify (native platform support), Google (Shopping and AI Mode integration)
• Endorsers: Visa, Best Buy, Target, Walmart, Flipkart, Macy's, The Home Depot, Zalando
• Payment handlers: Stripe, Adyen, Visa, Mastercard, American Express, PayPal
• Agents: Google Gemini, plus any MCP-compatible agent
• Development model: Open specification, public GitHub, reference implementations

#ACP Ecosystem

• Platform: Amazon (primary), with third-party sellers through 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
• Development model: Amazon-controlled specification, AWS SDKs

#Reach

ACP has an immediate advantage in merchant count — every Amazon Marketplace seller is automatically ACP-enabled. UCP has stronger backing from independent merchants and platforms outside Amazon's ecosystem. You can browse verified UCP merchants in the registry.

#When to Choose UCP

Choose UCP if your agent needs to:

• Work across platforms — not just Amazon. UCP covers Shopify, WooCommerce, BigCommerce, and independent retailers
• Support flexible payments — consumers pay with their preferred method, not just Amazon Pay
• Maintain merchant relationships — you're building for a retailer who doesn't want transactions flowing through Amazon
• Operate internationally — UCP's payment-handler flexibility supports region-specific payment methods
• Stay vendor-neutral — your agent's commerce capabilities aren't tied to one company's platform

#When to Choose ACP

Choose ACP if your agent:

• Prioritizes simplicity — one endpoint, one catalog, faster time to market
• Targets Amazon's catalog — your users primarily want Amazon products
• Needs fulfillment logistics — Amazon's FBA network is unmatched for Prime shipping
• Wants minimal payment complexity — Amazon Pay handles everything

#Can You Support Both?

Yes. The protocols aren't mutually exclusive. An agent can use UCP for independent merchants and ACP for Amazon's catalog, routing to whichever protocol the merchant supports. The Product Discovery API can help agents find UCP merchants for products that aren't on Amazon.

The key insight: Amazon dominates online retail in some categories but is a minority player in others. A well-built shopping agent should reach merchants wherever they are.

#The Bigger Picture

Two competing protocols is healthy for the ecosystem. Competition drives both specifications to improve and reduces the risk of single-protocol capture.

For more on how UCP, MCP, and A2A protocols work together, see the future of agentic commerce. The most likely long-term outcome is coexistence — similar to how REST and GraphQL both thrive. UCP will likely dominate the open web and independent commerce. ACP will dominate within Amazon's ecosystem. Smart agent developers will support both.

What matters most: agentic commerce is happening. 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.

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To see UCP adoption in action, browse the top UCP-enabled merchants in 2026 or read the latest state of the UCP ecosystem. If you're ready to build, our guide covers 5 things you can build with UCP today.

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Explore verified UCP merchants, tools, and platforms in the UCP Registry. Use the Product Discovery API to search across all stores.