The Agentic Commerce Protocol
How AI agents securely complete purchases on behalf of users — a complete guide to ACP (OpenAI + Stripe) and UCP (Google), the open standards powering agentic checkout in 2026.
What Is an Agentic Commerce Protocol?
An agentic commerce protocol is a standardized technical specification that defines how AI agents communicate with retailers to initiate and complete purchases — without human intervention at every step, and without exposing sensitive payment credentials to the AI.
Think of it like HTTP for the web — a shared language that allows different systems (AI agents, retailer backends, payment processors) to communicate reliably and securely. Without a protocol, every AI platform would need custom integrations with every retailer. With a protocol, a single implementation works everywhere that supports the standard.
In 2025–2026, two major protocols emerged: ACP from OpenAI and Stripe, and UCP from Google. Together, they define how AI-driven commerce will work for the next decade.
ACP and UCP:
Protocol Snapshot
This page explains how the protocols work. For a head-to-head decision table, see the UCP vs ACP comparison.
Agentic Commerce Protocol
By OpenAI + Stripe · Open Source (Apache 2.0)
Platforms Using ACP
ACP defines four core endpoints: Create Checkout, Update Checkout, Complete Checkout, and Cancel Checkout. The Shared Payment Token (SPT) lets Stripe process payments without AI agents ever seeing card details.
Universal Commerce Protocol
By Google · Proprietary
Platforms Using UCP
UCP has broader scope than ACP — covering product discovery and availability, not just checkout. Merchants implement UCP by creating a manifest at /.well-known/ucp.json.
ACP vs. UCP: Quick Reference
How ACP Works: The Checkout Flow
User expresses purchase intent
Shopper asks ChatGPT or Copilot to buy a specific product. The AI agent confirms availability and pricing with the merchant API.
Create Checkout (POST /checkouts)
Agent calls the merchant's ACP endpoint with the product SKU and variant. Merchant returns a checkout session with a price quote and order summary.
Shared Payment Token issued
Stripe issues a Shared Payment Token (SPT) to the AI platform using the user's saved Stripe payment method. The token never exposes actual card details to the AI agent.
Complete Checkout (POST /checkouts/{id}/complete)
Agent sends the SPT to the merchant's ACP endpoint. Stripe processes the payment. Merchant confirms the order and returns confirmation details.
Order confirmed in chat
The AI agent presents the confirmed order details in the conversation. No redirect, no external browser window — the purchase is fully complete inside the chat.
How to Integrate Agentic Commerce Protocols
There are two paths: DIY integration with each platform's API, or using Brambles.ai to handle the protocol layer automatically.
Direct Integration
For developers who want full control over their ACP/UCP implementation.
For ACP (ChatGPT + Copilot):
- 1.Apply at chatgpt.com/merchants
- 2.Build ACP REST endpoints per the OpenAI docs
- 3.Integrate Stripe for SPT payment handling
- 4.Microsoft Copilot uses same ACP — minimal extra work
For UCP (Google):
- 1.Join the UCP waitlist
- 2.Create
/.well-known/ucp.jsonmanifest - 3.Follow Google's UCP docs
- 4.Shopify merchants: enable natively from Shopify admin
Via Brambles.ai
Skip the protocol implementation entirely. Brambles.ai handles ACP and UCP compatibility for you.
- One integration — Brambles.ai handles protocol compliance
- Publishers: install plugin or script tag, done
- Retailers: connect catalog, deploy widget, done
- ACP + UCP compatible — your content/products appear everywhere
- No engineering resources required
How Agentic Commerce Protocols Stay Secure
Shared Payment Tokens (ACP)
Stripe issues tokens that represent payment authorization without exposing card details. AI agents never see actual payment credentials.
Protocol-Level Privacy (UCP)
Google's UCP requires merchants to handle user data in accordance with its privacy specifications. User identity is managed by Google Pay.
Open Source Auditing (ACP)
ACP is published under Apache 2.0, allowing public security auditing of the specification. No proprietary black boxes.
Protocol Questions Answered
What is the difference between UCP and ACP?
UCP and ACP are two competing agentic commerce protocols. ACP (Agentic Commerce Protocol) by OpenAI and Stripe was launched in September 2025, is open source under Apache 2.0, focuses purely on checkout, uses Stripe Shared Payment Tokens, and powers ChatGPT Instant Checkout and Microsoft Copilot. UCP (Universal Commerce Protocol) by Google was launched January 2026, is proprietary, covers both discovery and checkout, uses Google Pay, charges no transaction fee, and powers Google AI Mode, Gemini, Shopify (native), Walmart, Wayfair, and Target. Most retailers should plan to support both since they reach different agent ecosystems.
UCP vs ACP — which should I implement first?
If you're a Shopify merchant, UCP is already native — enable it from the Shopify admin and you're live with Google AI Mode and Gemini. If you're on WooCommerce, BigCommerce, Squarespace, Wix, or Etsy, ACP is your priority since those platforms ship native ACP support and unlock ChatGPT plus Microsoft Copilot. For maximum agent reach, implement both. Brambles.ai's Agentic Commerce Module is compatible with both protocols, so you don't have to choose or implement either yourself.
What is the Agentic Commerce Protocol (ACP)?
The Agentic Commerce Protocol (ACP) is an open-source standard developed by OpenAI and Stripe that enables AI agents to complete purchases on behalf of users. It defines a RESTful interface for initiating, updating, and completing checkout flows without exposing payment credentials. ACP is used by ChatGPT Instant Checkout, Microsoft Copilot, and several major ecommerce platforms.
What is Google's Universal Commerce Protocol (UCP)?
The Universal Commerce Protocol (UCP) is Google's own agentic commerce standard, launched in January 2026. Unlike ACP which focuses on checkout, UCP has broader scope covering discovery and purchasing through Google AI Mode and Gemini. It uses Google Pay and does not charge merchants a transaction fee. Shopify, Walmart, Wayfair, and Target are among early UCP adopters.
Do I need to implement both ACP and UCP?
For maximum coverage, yes — but you can start with one. Google and ChatGPT are the highest-priority platforms to integrate with first, as they have the largest user bases for shopping. If you're a Shopify merchant, Shopify is building native integrations with both protocols so you won't need custom technical work.
How does Brambles.ai relate to ACP and UCP?
Brambles.ai's Agentic Commerce Module is built on top of these protocols and compatible with both. When publishers and retailers deploy our platform, their products and content become discoverable and transactable within AI agents — without needing to implement ACP or UCP directly themselves. Brambles.ai handles the protocol layer.
Is the Agentic Commerce Protocol secure?
Yes. ACP is designed with security as a core principle. It uses Stripe's Shared Payment Tokens (SPT), which means AI agents never handle actual payment credentials. The token system allows Stripe to process payments while keeping sensitive card information fully isolated from the AI layer. Both ACP and UCP have privacy and security requirements built into the protocol specification.
Skip the Protocol Work
Brambles.ai handles ACP and UCP compliance for you. Publishers and retailers get agentic commerce without engineering overhead.