UCP vs ACP: Understanding the Two Major Agentic Commerce Protocols in 2026

The rise of AI shopping agents has created a new frontier in e-commerce infrastructure. Two major protocols have emerged to standardize how AI agents interact with online merchants: Universal Commerce Protocol (UCP) and Agentic Commerce Protocol (ACP). Understanding the difference between these standards is critical for merchants, developers, and anyone building in the agentic commerce space.

What is UCP (Universal Commerce Protocol)?

Universal Commerce Protocol is an open-source standard launched in January 2026 at NRF by Google. Co-developed with Shopify and backed by over 20 global partners including Walmart, Target, Etsy, Wayfair, Visa, Mastercard, Stripe, Adyen, American Express, Best Buy, Flipkart, Macy's, The Home Depot, and Zalando, UCP provides a comprehensive framework for the entire shopping lifecycle.

UCP covers discovery, consideration, cart management, checkout, payment processing, post-purchase support, and loyalty programs. It's designed to be surface-agnostic, working seamlessly across Google Search AI Mode, the Gemini app, and any AI agent platform.

The protocol is also protocol-agnostic, supporting REST APIs, Model Context Protocol (MCP), and Agent-to-Agent (A2A) communication. The specification is publicly available on GitHub and at ucp.dev.

What is ACP (Agentic Commerce Protocol)?

Agentic Commerce Protocol is an open standard maintained by OpenAI and Stripe, launched in October 2025. It powers ChatGPT's "Instant Checkout" feature and focuses specifically on checkout and transaction flows within conversational AI experiences.

ACP uses a REST API tightly coupled to ChatGPT's interface and Stripe's payment rails. The protocol is currently live with Etsy sellers, with Shopify merchants including Glossier, SKIMS, Spanx, and Vuori coming soon. With 50 million daily shopping queries on ChatGPT and a 36 percent purchase rate among platform users, ACP has demonstrated significant early traction in conversational commerce.

UCP vs ACP Comparison Table

Key Differences: UCP vs ACP

Scope and Coverage

The most fundamental difference is scope. UCP is a broad lifecycle standard covering the entire customer journey from discovery to post-purchase support. ACP is checkout-focused, optimizing specifically for transaction completion within conversational interfaces.

If you need an AI agent to discover products, compare options, manage a cart, complete checkout, handle returns, and manage loyalty points, UCP provides the comprehensive framework. If you need to enable instant checkout within ChatGPT conversations, ACP is purpose-built for that experience.

Discovery Model

UCP uses decentralized discovery. Merchants publish their capabilities at /.well-known/ucp on their own domain, allowing any AI agent to discover and interact with them without centralized approval. This follows the same philosophy as robots.txt and other web standards.

ACP uses centralized discovery. Merchants apply through OpenAI and are approved before their products appear in ChatGPT. This curated approach provides quality control but limits which merchants can participate in the ChatGPT shopping experience.

Multi-Agent Architecture

UCP is designed for multi-agent and multi-surface experiences. The same UCP implementation works across Google Search, Gemini, third-party AI agents, and future AI platforms. This future-proofs merchant investments in agentic commerce infrastructure.

ACP is optimized primarily for the ChatGPT experience. While technically it could be adopted by other platforms, the protocol design and payment integration are closely tied to OpenAI's product roadmap.

Protocol Flexibility

UCP supports multiple communication protocols including REST, MCP (Model Context Protocol), and A2A (Agent-to-Agent). This flexibility allows merchants to choose the integration approach that best fits their technical architecture and enables dynamic capability negotiation between agents and merchants.

ACP uses a REST API as its primary interface, providing a straightforward integration path for merchants already familiar with REST patterns and Stripe's payment infrastructure.

Payment Architecture

UCP uses AP2 (Agent Payments Protocol) for payment authorization with Google Pay as the primary payment method and PayPal support planned. Critically, the merchant remains the Merchant of Record and retains full customer relationship ownership.

ACP uses delegated payment tokens that are single-use, time-bound, and amount-restricted. These tokens are processed through Stripe's infrastructure, providing strong security guarantees for conversational checkout experiences.

Why Merchants Should Care

Most major retailers will adopt both protocols. This isn't a winner-takes-all situation. UCP and ACP are complementary standards solving different parts of the commerce journey.

Merchants adopting UCP gain access to Google's AI surfaces and any third-party AI agent that implements the protocol. This provides broad reach across the emerging agentic commerce ecosystem. The comprehensive lifecycle coverage means one implementation supports discovery, checkout, post-purchase, and loyalty.

Merchants adopting ACP gain access to ChatGPT's 50 million daily shopping queries and high-intent conversational commerce traffic. The tight integration with Stripe simplifies payment processing for merchants already using Stripe.

The strategic approach for most merchants is to implement both protocols, gaining the reach of UCP and the high-conversion ChatGPT traffic from ACP.

The Technical Architecture Differences

From a technical implementation perspective, UCP requires publishing a manifest at /.well-known/ucp that describes merchant capabilities and API endpoints. AI agents discover this manifest and negotiate capabilities dynamically. This decentralized approach means no approval process, but merchants are responsible for protocol compliance.

ACP requires going through OpenAI's merchant application process and integrating with Stripe's payment infrastructure. The approval process ensures quality but adds friction to merchant onboarding. Once approved, merchants benefit from ChatGPT's massive built-in audience.

The Future of Agentic Commerce Standards

The emergence of UCP and ACP signals that agentic commerce is moving from experimental to mainstream. The fact that Google, OpenAI, Shopify, Stripe, and major retailers are aligning behind standardized protocols indicates this is the future of online shopping.

In the next 12 months, expect to see widespread adoption of both protocols by major merchants. The UCP Market directory already tracks hundreds of UCP implementations, and ACP adoption is accelerating as more Shopify merchants come online.

The protocols will likely evolve and potentially converge on certain aspects over time. Industry standards often go through multiple iterations before settling on widely adopted patterns. The important thing for merchants is to begin implementing at least one protocol now to gain experience with agentic commerce.

Choosing Between UCP and ACP

For merchants deciding where to start, consider your strategic priorities. If broad reach across multiple AI platforms is the goal, start with UCP. If high-conversion ChatGPT traffic is the priority, start with ACP. If resources allow, implement both to maximize reach across the agentic commerce landscape.

For developers building AI shopping agents, supporting both protocols provides access to the widest merchant ecosystem. UCP's flexibility makes it easier to build generalized shopping agents, while ACP provides a direct path to ChatGPT integration.

Conclusion

UCP and ACP represent different philosophies in agentic commerce: comprehensive lifecycle coverage with decentralized discovery versus checkout-optimized with curated experiences. Both have strong backing from tech giants and major merchants. Both are growing rapidly.

The winning strategy for most merchants is not choosing one over the other, but thoughtfully implementing both to maximize reach across the emerging agentic commerce ecosystem. The future of AI shopping will likely involve multiple protocols working together, much like the modern web supports multiple standards simultaneously.

Understanding these protocols now positions merchants and developers to succeed as agentic commerce becomes the dominant shopping paradigm in 2026 and beyond.