UCP vs ACP: Which Agentic Commerce Protocol Should Retailers Implement?

Two competing protocols now define how AI agents will shop on behalf of consumers. OpenAI and Stripe’s Agentic Commerce Protocol (ACP) launched in September 2025. Google’s Universal Commerce Protocol (UCP) launched in January 2026. Both are open source under Apache 2.0, and both will shape the $3 trillion to $5 trillion global agentic commerce market projected by 2030.

I’ve analyzed both protocols across scope, architecture, payments, integrations, and ecosystem adoption. This comparison covers what matters for retailers evaluating implementation. Read to the end for specific recommendations based on your existing infrastructure.

Quick Verdict

Don’t choose. Layer them. Use ACP for speed today, and build UCP for scale tomorrow.

ACP has a three-month head start and powers ChatGPT’s 700 million weekly users. UCP covers the full commerce lifecycle and connects to Google’s search ecosystem. Walmart and Shopify are implementing both. This isn’t about picking a winner. It’s about sequencing: ACP gets you live in weeks, UCP builds the foundation for years.

What’s Covered

1. At a Glance Comparison
2. Key Differences
3. My Analysis
4. Scope and Coverage
5. Technical Architecture
6. Payment Systems
7. Ecosystem Adoption
8. Integration Effort
9. Cost Comparison
10. When to Choose Each
11. Comparison Summary
12. Final Verdict

At a Glance

Key Differences

1. Scope of coverage. ACP handles checkout transactions only. UCP handles discovery, checkout, order management, and post-purchase support. ACP solves one problem well; UCP attempts to standardize the entire journey.

2. Payment approach. ACP uses Stripe’s Shared Payment Tokens, which are single-use, time-bound, and merchant-scoped. UCP uses the Agent Payments Protocol (AP2) with cryptographic mandate chains that create audit trails from intent to payment.

3. Integration path. ACP is Stripe-native. If you already use Stripe, enabling agentic payments takes one line of code. UCP integrates through Google Merchant Center and offers more flexibility across payment processors.

4. Production maturity. ACP has three months of live transaction processing. ChatGPT Instant Checkout with Etsy has been processing real orders since September. UCP launched at NRF 2026 with pilots announced but no production volume yet.

5. Ecosystem reach. UCP connects to Google Search, which still drives the majority of product discovery. ACP connects to ChatGPT, which processes 50 million shopping queries daily. Different platforms, different customer segments.

My Analysis

I’ve been tracking agentic commerce since OpenAI announced Operator in late 2024. The protocol war was inevitable once ChatGPT started processing shopping queries at scale. What surprised me was how fast Google responded with broader scope.

The strategic positioning is clear. OpenAI and Stripe built ACP to capture transaction revenue as AI becomes a shopping interface. Google built UCP to protect its search and advertising business by owning the infrastructure layer. Neither company is being altruistic with “open source.” Both are racing to become the default before the market fragments.

For marketing leaders watching this space, the protocol debate matters less than what it signals: AI agents are becoming a commerce channel with real transaction volume. I’ve written before about how to build AI marketing agents that connect to these systems. The retailers who treat protocols as infrastructure investment will capture share. Those who wait for a “winner” will build integrations under competitive pressure later.

Scope and Coverage

Winner: UCP

UCP covers the entire commerce lifecycle from product discovery through post-purchase support. It organizes commerce into Services (vertical domains), Capabilities (functional areas like Checkout), and Extensions (optional features). At launch, UCP supports Checkout, Identity Linking, and Order Management capabilities with roadmap items for catalog management and loyalty programs.

ACP defines four core endpoints: Create Checkout, Update Checkout, Complete Checkout, and Cancel Checkout. That’s the complete specification. It’s deliberately narrow, solving the transaction moment without prescribing how discovery or post-purchase should work.

Our take: ACP’s narrow scope means faster implementation but more custom work for everything outside checkout. UCP’s broader scope requires more upfront investment but provides fuller coverage. For teams building long-term infrastructure, UCP’s architecture is more forward-looking.

Technical Architecture

Winner: Tie

ACP’s architecture reflects Stripe’s payment processing DNA. It’s a RESTful interface with four endpoints, webhook notifications for order updates, and Shared Payment Tokens for secure credential handling. You can also implement it as an MCP server for tighter agent integration.

UCP’s architecture reflects Google’s platform thinking. Services contain Capabilities which support Extensions. This modularity means you implement only what you need. The protocol supports REST, MCP, and Google’s A2A for agent-to-agent communication.

Our take: ACP is simpler to understand and implement. Four endpoints, familiar REST patterns, and Stripe’s existing SDKs. UCP is more complete but requires understanding multiple abstraction layers. Choose based on your team’s capacity for complexity.

Payment Systems

Winner: ACP

Both protocols solve the same security problem: AI agents need to initiate payments without exposing user credentials. ACP uses Shared Payment Tokens that are single-use, time-bound, and scoped to specific merchants and amounts. Stripe Radar provides fraud detection signals. The system is production-tested with millions of transactions.

UCP uses AP2 Mandates with cryptographic proofs. An Intent Mandate defines agent permissions. A Cart Mandate captures buyer approval. A Payment Mandate authorizes the transaction. This chain creates non-repudiable evidence of consent at each step, but it’s more complex to implement.

Our take: ACP’s payment model is battle-tested and Stripe-native. If you’re already on Stripe, it’s the obvious choice. UCP’s mandate chain is theoretically more robust but has no production track record yet. For most retailers, ACP wins on proven reliability.

Ecosystem Adoption

Winner: UCP

UCP launched with the broadest coalition in e-commerce history. Co-developers include Shopify, Walmart, Target, Etsy, and Wayfair. Payment endorsers include Mastercard, Visa, American Express, Stripe, PayPal, and Adyen. Retail endorsers include Best Buy, Home Depot, Macy’s, and Sephora.

ACP has a three-month head start in production. Etsy’s entire US seller base (over 5 million sellers) has been automatically enrolled since September. Over one million Shopify merchants are eligible. Stripe’s Agentic Commerce Suite launched in December with URBN, Ashley Furniture, Coach, and Kate Spade.

Our take: UCP has broader industry backing. ACP has more production traction. The fact that Stripe, Shopify, and Etsy support both protocols tells you the industry expects coexistence. Neither will “win” in the near term.

Integration Effort

Winner: ACP

For Stripe merchants, ACP integration is remarkably simple. Enable agentic payments with one line of code. Shopify merchants using Shopify Payments are automatically eligible with no integration required. Etsy sellers were enrolled automatically when ACP launched.

UCP offers two paths: Native (use Google’s checkout interface with your Merchant Center feeds) or Embedded (maintain your custom checkout while enabling agentic transactions). Both require more configuration than ACP’s Stripe-native approach, though Shopify is building admin-level enablement.

Our take: If you’re already on Stripe, ACP takes days to implement. UCP takes weeks to months depending on your integration approach. For teams prioritizing speed to market, ACP wins decisively.

Cost Comparison

Value analysis: Both protocols are free to use. The real cost is integration effort. ACP’s Stripe-native approach means minimal engineering time for existing Stripe merchants. UCP’s broader scope means more upfront work but potentially less custom development for full-lifecycle features like order management and returns.

Verified January 2026. Check official documentation for current requirements.

When to Choose Each

When to Choose UCP

• Google Search and Gemini are primary discovery channels
• You need full lifecycle support including order management
• You want flexibility across multiple payment processors
• You’re building long-term agentic commerce infrastructure
• You need custom checkout experiences with brand control

When to Choose ACP

• You’re already using Stripe for payment processing
• You’re on Shopify or Etsy and want automatic enablement
• ChatGPT is a significant traffic source for your audience
• You prioritize speed to market over comprehensive features
• Your checkout is already optimized and you don’t want to rebuild

Comparison Summary

Reading the scores: ACP wins on speed metrics (initial integration, developer experience, production maturity). UCP wins on depth metrics (scope, architecture, ecosystem). This is why most enterprises are layering both: ACP for immediate ChatGPT coverage, UCP for long-term infrastructure.

Final Verdict

Layer both protocols. This isn’t about picking winners. It’s about building infrastructure that captures customers wherever they shop.

ACP wins on speed to market and production maturity. Three months of live transactions, minimal integration effort for Stripe merchants, and automatic enablement for Shopify and Etsy. If you need to move fast, start here.

UCP wins on scope and ecosystem coalition. Full lifecycle coverage, broad industry support, and connection to Google’s search traffic. If you’re building infrastructure for the next decade, UCP’s architecture is more comprehensive. For a deeper technical dive, see my complete UCP implementation guide.

Choose UCP first if: Google is your primary discovery channel, you need full lifecycle support beyond checkout, or you want flexibility across payment processors. The broader coalition suggests UCP will be the long-term standard.

Choose ACP first if: You’re already on Stripe, ChatGPT is relevant to your audience, or you need something live in weeks rather than months. The production track record provides confidence.

Best of both: Implement ACP now for immediate ChatGPT coverage, then add UCP as it matures. This is exactly what Walmart and Shopify are doing. Follow the enterprise playbook.

FAQ

What is the main difference between UCP and ACP?

UCP covers the entire commerce lifecycle from product discovery through post-purchase support, while ACP focuses specifically on the checkout transaction layer. UCP is backed by Google and Shopify. ACP is backed by OpenAI and Stripe.

Which protocol should retailers implement first?

Most retailers will need both protocols. ACP has a three-month head start with ChatGPT’s 700 million weekly users. UCP provides access to Google AI Mode and Gemini. Major retailers like Walmart and Shopify are implementing both.

How do the payment systems differ between UCP and ACP?

ACP uses Stripe’s Shared Payment Tokens (SPTs), which are single-use, time-bound tokens scoped to specific merchants. UCP uses the Agent Payments Protocol (AP2) with cryptographic Mandates that create audit trails from intent to payment.

Are UCP and ACP compatible with each other?

The protocols are designed to coexist rather than compete directly. UCP explicitly supports interoperability with existing protocols including A2A and MCP. Many payment processors like Stripe and PayPal endorse both protocols.

What is the integration effort for each protocol?

ACP offers very low integration effort for Stripe merchants, requiring as little as one line of code. Shopify and Etsy merchants are automatically eligible. UCP integration varies by approach but offers native SDKs and Merchant Center integration.

Which AI platforms support each protocol?

ACP powers ChatGPT Instant Checkout and is being adopted by Microsoft Copilot and Perplexity. UCP powers Google AI Mode in Search and the Gemini app. Both protocols are designed to be platform-agnostic.