Universal Commerce Protocol vs Closed Marketplaces: Which Will Win the AI Shopping Revolution?

The way people shop online is changing fast. AI shopping agents can now handle entire purchases, from finding products to completing checkout. But two very different approaches are fighting to control this future: open protocols like Google's Universal Commerce Protocol (UCP) and closed marketplaces like Amazon.

This choice will shape how you discover products, where AI agents can shop, and whether merchants control their customer relationships. The stakes are enormous—experts predict agentic commerce will reach $3-5 trillion by 2030.

Let's explore both approaches and what they mean for shoppers, retailers, and the future of online commerce.

What Is the Universal Commerce Protocol?

The Universal Commerce Protocol is an open standard launched by Google and Shopify in January 2026 that enables AI agents to complete purchases across different platforms without custom integrations. Think of it like HTTP for the web, but for commerce.

UCP creates a common language that lets AI agents discover products, manage shopping carts, process payments, and handle post-purchase support across any participating merchant. More than 20 partners across the ecosystem have endorsed UCP, including Shopify, Etsy, Wayfair, Target, Walmart, Adyen, American Express, Stripe, and Visa.

How UCP Works

UCP collapses N x N complexity into a single integration point for all consumer surfaces. Instead of merchants building separate connections for Google AI Mode, Gemini, ChatGPT, and every other AI agent, they integrate once with UCP.

The protocol handles:

• Product discovery and catalog management
• Dynamic checkout sessions with complex cart logic
• Multiple payment methods through flexible handlers
• Tax calculations and fulfillment options
• Order tracking and post-purchase events

Merchants remain the seller of record. They control pricing, inventory, customer data, and the checkout experience.

What Are Closed Marketplaces?

Closed marketplaces are self-contained environments where a single company controls all rules, from data access to payment processing. Platforms like Amazon, eBay, and retail media networks operate as walled gardens.

In these ecosystems, merchants must use the platform's tools, follow its policies, and accept limited visibility into customer data. The platform owns the customer relationship and controls how products appear in search results and AI agent recommendations.

The Walled Garden Approach

Amazon has something Google and Facebook don't—purchase intent data, knowing what users buy, from whom, and how often. This data creates a powerful competitive advantage.

Amazon generates over $20 billion in ad revenue through Amazon Ads, featuring unique walled garden attributes while controlling purchase data from 18.5 purchases made every second.

The closed marketplace model offers:

• Complete control over the user experience
• Proprietary data that competitors cannot access
• Self-service advertising platforms
• Built-in trust from established brand recognition

Key Differences: UCP vs Closed Marketplaces

The Battle for AI Shopping Dominance

Research from leading consulting firms suggests the global agentic commerce market could reach $3-5 trillion by 2030. Both approaches want to capture this massive opportunity.

Google and OpenAI's Open Protocol Strategy

UCP will soon power a new checkout feature on eligible Google product listings in AI Mode in Search and the Gemini app, allowing U.S. shoppers to check out from eligible retailers right as they're researching.

OpenAI took a similar approach. OpenAI launched Instant Checkout in ChatGPT, powered by the Agentic Commerce Protocol built with Stripe, allowing U.S. users to buy directly from U.S. Etsy sellers and over a million Shopify merchants.

Both protocols share key principles:

• Open standards that work across platforms
• Merchants control customer relationships
• Compatible with existing payment processors
• Built for agent-to-agent communication

Amazon's Walled Garden Defense

Unlike many retailers that have partnered with third-party AI companies like OpenAI, Amazon has blocked off its site from outside agents, likely to protect its $56 billion advertising business.

Amazon doesn't need UCP. It already has:

• Stored payment credentials for millions
• Consumer trust and habitual usage
• 40% of U.S. e-commerce spending
• 90% of shoppers starting searches on Amazon.com

The company sued Perplexity for improperly accessing its site, showing how seriously it takes this competitive threat.

Advantages of Open Protocols Like UCP

For Merchants

Control and Flexibility Merchants maintain ownership of customer data and relationships. They choose their payment provider, design their checkout flow, and set their own policies.

Wider Reach UCP reduces integration complexity and removes technical barriers, enabling businesses to participate in agentic commerce across multiple AI platforms with one integration.

Lower Costs No platform fees on each transaction. Merchants pay their chosen payment processor directly.

Brand Identity UCP allows merchants to define their own extensions for specialized requirements like custom fulfillment, maintaining their unique value proposition.

For Shoppers

Choice and Competition AI agents can compare products across merchants, not just within a single marketplace. This drives better prices and selection.

Consistent Experience Shop from any AI interface—ChatGPT, Google AI Mode, Gemini—with the same smooth checkout process.

Privacy Your shopping data isn't locked in one company's ecosystem. Agents work on your behalf across the open web.

For the Ecosystem

Innovation New payment methods grow into the ecosystem without committee votes or core version bumps through UCP's payment handler system.

Interoperability UCP is compatible with Agent Payments Protocol, Agent2Agent, and Model Context Protocol, creating a truly connected commerce environment.

Advantages of Closed Marketplaces

For Merchants

Built-in Traffic Marketplaces provide immediate access to millions of active shoppers. No need to drive your own traffic.

Trust by Association Amazon already has stored payment credentials, consumer trust, and habitual usage, making conversions easier.

Simplified Operations One platform handles payments, fraud detection, fulfillment options, and customer service tools.

Powerful Targeting Walled gardens offer the ability to segment audiences based on user data including demographics, interests, behaviors, and past purchases.

For Shoppers

Familiarity and Speed Amazon captures 40% of all U.S. e-commerce spending, and 90% of its shoppers begin their searches directly on Amazon.com. People know how it works.

Buyer Protection Established dispute resolution, return policies, and customer service.

Unified Experience Everything in one place—search, reviews, checkout, tracking, and support.

For Platforms

Data Moat Walled gardens leverage unique first-party data relationships with users, creating environments where advertisers must operate within proprietary systems.

Revenue Control Platforms charge fees on transactions, advertising, and premium placements, creating multiple revenue streams.

The Current State of AI Shopping in 2026

Market Adoption

eMarketer expects AI platforms to account for 1.5% of total retail e-commerce sales in 2026, or $20.9 billion in spending—nearly quadruple 2025's figures.

Forrester research predicts one-quarter of shoppers will use specialty retail chatbots in 2026.

Consumer Behavior

38% of consumers use AI when shopping today, and 80% expect to use it more, primarily for comparing options and getting decision support.

The fastest adoption is happening in:

• Price comparisons and deal-finding
• Product research and credibility checks
• Household replenishment
• Review validation

Platform Developments

Google's UCP Rollout As of early 2026, UCP-powered native checkout is actively rolling out to eligible retailers in the United States, with major platforms like Shopify among the first to integrate.

Payment currently centers around Google Wallet, with PayPal and other providers coming soon. International expansion is confirmed with key partners in Europe and Asia endorsing the protocol.

OpenAI's Instant Checkout ChatGPT users in the U.S. can now buy directly from U.S. Etsy sellers, with over a million Shopify merchants coming soon. OpenAI takes a small fee on completed purchases but doesn't influence product rankings.

Closed Platform Responses Major retailers are building their own AI shopping features. Walmart's Sparky, Amazon's Rufus, and Target's conversational AI keep shoppers within their ecosystems.

Challenges for Open Protocols

Merchant Adoption Hurdles

Technical Integration While simpler than building multiple platform connections, UCP still requires development resources and testing.

Data Standardization Agents need granular information—not just basic attributes, but detailed descriptions of fit, quality, durability, shipping timelines and inventory.

Quality Control Merchants must ensure their product feeds provide accurate, comprehensive data for AI agents to make good recommendations.

Trust and Security

Payment Safety UCP uses tokenized payments and verifiable credentials as a secured way to communicate between agents and business backends.

But consumers need confidence that their payment information is protected across many merchants and AI agents.

Fraud Prevention Each merchant must handle fraud detection. This is harder than relying on a marketplace's established systems.

Fragmentation Risk

If multiple open protocols compete (UCP, OpenAI's Agentic Commerce Protocol, others), merchants face the same integration burden the protocols aimed to solve.

Challenges for Closed Marketplaces

Platform Dependence

Limited Control Marketers must manage between five and nine different retail media networks, each with its own interface, metrics, and limitations.

Algorithm Changes Platforms can change ranking algorithms, fees, or policies at any time. Merchants have no recourse.

Data Access Walled gardens prevent data from leaving in a format that's interoperable with other ecosystems.

Competition Concerns

Platform Favoritism Marketplaces can promote their own products over merchant offerings.

Fee Pressure Transaction fees, advertising costs, and premium placement charges reduce merchant margins.

Customer Ownership Merchants never fully own customer relationships, limiting long-term brand building.

AI Agent Exclusion

Amazon blocked off its site from outside agents, creating tension as platforms jockey to control the future of AI-driven commerce.

This limits consumer choice. Shoppers using third-party AI agents cannot access products exclusively sold on closed platforms.

What This Means for Different Stakeholders

For Small Businesses

Open Protocols Advantage Small merchants gain access to AI shopping channels without the high advertising costs of marketplace competition. One UCP integration reaches multiple AI agents.

Closed Marketplace Reality PayPal's ACP server will bring the product catalogs of small businesses to ChatGPT commerce in 2026, creating opportunities for businesses that couldn't afford complex integrations.

Many small sellers still need marketplace traffic and trust. The Amazon brand carries weight that helps conversions.

For Large Retailers

Hybrid Strategy Target and Kroger use a hybrid approach, straddling a walled garden mentality and the open programmatic web.

Major retailers can afford to maintain their own e-commerce sites, integrate with UCP, AND sell on marketplaces. This maximizes reach while maintaining brand control where possible.

Direct Competition Large retailers with established brands benefit most from open protocols. They can compete with Amazon by making their products discoverable across all AI agents.

For Consumers

Best of Both Worlds Consumers will likely use both approaches. Quick, familiar purchases happen on Amazon. Researched, considered purchases leverage AI agents comparing across open protocol merchants.

Privacy Considerations Open protocols distribute your shopping data across merchants and AI agents. Closed marketplaces centralize it in one company's hands. Neither approach is perfect for privacy.

For AI Platform Companies

Access to Commerce Stripe and OpenAI created the Agentic Commerce Protocol as a shared language between businesses and AI agents, enabling merchants to sell through AI agents while retaining full control.

Google, OpenAI, and others benefit when merchants integrate with their protocols. More merchants mean more shopping utility for their AI agents, attracting more users.

The Future: Coexistence or Winner-Take-All?

The Coexistence Scenario

Both approaches will likely survive. Closed marketplaces excel for certain product categories and shopping missions. Open protocols enable discovery and comparison across the broader web.

Where Marketplaces Win

• Commodity products where price is king
• Household replenishment and recurring purchases
• Shoppers prioritizing speed and simplicity
• Categories requiring heavy curation and trust

Where Open Protocols Win

• Considered purchases requiring comparison
• Brand-loyal shoppers
• Specialty and niche products
• Merchants wanting direct customer relationships

The Tipping Point Factors

Consumer Adoption Rate IDC projections show agentic AI will represent 10-15% of IT spending in 2026 and grow to 26% of budgets by 2029.

If AI agent shopping becomes the default for most purchases, open protocols gain an advantage. If adoption stays limited to specific use cases, marketplaces maintain their dominance.

Data Quality Shopping agents are only as good as the data they can access, and GenAI knows far more about the shopper than Google ever did.

The platform that provides AI agents with the best product data wins consumer trust. This could favor marketplaces with structured, consistent data or open protocols if merchants invest in rich product feeds.

Platform Lock-In Consumer habits are hard to change. Amazon doesn't need to worry about its retail empire being upended yet because it already has stored payment credentials, consumer trust and habitual usage.

Regulatory Influence

Governments are watching. If regulators view closed marketplaces as anti-competitive, they may mandate open access for AI agents. This would accelerate UCP-style protocols.

Conversely, privacy and security concerns could favor established, trusted marketplaces over distributed open systems.

Preparing for the AI Shopping Future

For Merchants

Get Your Data Ready Whether you choose open protocols, marketplaces, or both, AI agents need structured, detailed product information.

Create comprehensive product feeds with:

• Detailed descriptions and specifications
• High-quality images and videos
• Accurate pricing and inventory
• Shipping options and timelines
• Customer reviews and ratings

Choose Your Strategy Evaluate where your customers are and where they're going. Agentic AI is likely to grow fastest in helping shoppers narrow choices, weigh tradeoffs, and reduce the effort involved in evaluating products.

Consider:

• Your target customer's shopping habits
• Your product category and price point
• Your resources for integration and maintenance
• Your brand strength and differentiation

Test and Learn If you're on a popular e-commerce platform like Shopify, there's a high chance they are working on or have already implemented UCP compatibility.

Start small with one or two channels. Measure results. Expand where you see traction.

For Shoppers

Understand the Tradeoffs Marketplace shopping is fast and familiar. Open protocol shopping via AI agents provides broader comparison and potentially better deals.

Your payment data is either centralized (marketplace) or distributed (open protocols). Consider which approach aligns with your privacy preferences.

Leverage Both Use marketplaces for routine purchases where you know what you want. Use AI agents for research and discovery when exploring options.

Stay Informed The AI shopping landscape is evolving rapidly. What works today may change tomorrow as platforms add features and policies shift.

The Verdict: Which Approach Will Dominate?

The honest answer? Both will succeed in different ways.

Closed marketplaces aren't going anywhere. Amazon's dominance is too strong, its convenience too compelling, and consumer habits too ingrained. Millions of shoppers will continue starting and ending their journeys within marketplace walls.

Open protocols will grow significantly. As AI agents become more capable and trusted, shoppers will increasingly use them for discovery and comparison. Merchants will embrace protocols that let them reach customers across platforms while maintaining brand control.

The real question isn't which approach wins, but how quickly open protocols capture share from search engines and walled gardens.

The global agentic commerce market could reach $3-5 trillion by 2030, with the U.S. B2C retail market alone seeing up to $1 trillion in orchestrated revenue from agentic commerce.

This massive opportunity will be split among:

• Established marketplaces defending their territory
• Open protocol platforms enabling cross-merchant shopping
• Hybrid retailers using both approaches strategically
• New entrants building AI-native shopping experiences

Getting Started Today

The future of AI-driven shopping is arriving now. Here's how to participate:

Merchants:

• Review your product data quality
• Check if your e-commerce platform supports UCP or Agentic Commerce Protocol
• Monitor traffic from AI sources
• Test one integration as a pilot

Consumers:

• Try AI shopping agents like ChatGPT's Instant Checkout or Google AI Mode
• Compare results with traditional marketplace shopping
• Provide feedback to improve recommendations

Platform Providers:

• Implement open protocol standards
• Prioritize data security and fraud prevention
• Focus on user experience and trust

The shift to agentic commerce represents the biggest change in online shopping since the rise of e-commerce itself. Understanding the difference between open protocols and closed marketplaces helps you make informed decisions about where to shop, where to sell, and what to build.

Both approaches offer value. The winners will be those who leverage the strengths of each while adapting quickly as the landscape evolves.