Two agentic commerce protocols have emerged: UCP (Universal Commerce Protocol, co-developed by Google and Shopify) and ACP (Agentic Commerce Protocol, by OpenAI and Stripe). They target different AI ecosystems with different philosophies. Here is how they compare.
| Dimension | UCP (Google + Shopify) | ACP (OpenAI + Stripe) |
|---|---|---|
| Scope | Full commerce lifecycle: discovery, comparison, cart, checkout, fulfillment, returns, loyalty | Primarily checkout-focused |
| Payment layer | Delegates to AP2 (payment-agnostic: any processor, any wallet) | Built-in via Stripe SPTs (Stripe Payment Tokens) |
| Transports | REST, JSON-RPC (MCP), A2A, Embedded (ECP) | REST, MCP |
| Post-purchase | Standardized: returns, tracking, loyalty, adjustments | Not in spec |
| Multi-merchant cart | Supported (Universal Cart API) | Single merchant per session |
| First deployment | Google Search AI Mode, Gemini (early access) | ChatGPT Instant Checkout (production) |
| Governance | Google-led coalition (50+ partners) | OpenAI + Stripe |
| Maturity | Early access (spec evolving) | Production (since Sep 2025) |
| Multi-agent | Native A2A delegation support | Application-layer orchestration |
| Embedded UI | ECP (Embedded Commerce Protocol) - bidirectional messaging, agent branding | Limited |
| Discovery | Decentralized via /.well-known/ucp |
Centralized via Stripe merchant onboarding |
| Industry expansion | Lodging, Food verticals announced | Commerce-only |
| Open source | Apache 2.0 at ucp.dev | OpenAI/Stripe controlled |
UCP is designed as a vendor-neutral, open standard. It does not prescribe a payment processor. It does not require a specific platform. It is decentralized - no central server, no central registry. Any merchant on any platform can implement UCP. Any agent on any framework can consume it. The governance model (reverse-domain naming) means vendors can extend the protocol without asking permission.
The trade-off: broader scope and more flexibility means more complexity. The spec is larger. There are more moving parts (transports, extensions, capabilities). And because it is earlier in maturity, there are fewer production deployments.
ACP is more tightly integrated. It ships with Stripe built in, which means payment handling is simpler (if you use Stripe). It is production-ready today on ChatGPT. It is focused on checkout, which means less surface area to implement.
The trade-off: you are buying into the OpenAI/Stripe ecosystem. The protocol is not payment-agnostic. Discovery is more centralized. If you want to use a non-Stripe processor, you are on your own.
The protocols are not mutually exclusive. A merchant can support both. The discovery mechanisms are independent.
| Aspect | UCP | ACP |
|---|---|---|
| Mechanism | /.well-known/ucp (decentralized) | Stripe merchant onboarding (centralized) |
| Caching | Both parties cache profiles | N/A |
| Version negotiation | Protocol + capability version negotiation | API version |
| Aspect | UCP | ACP |
|---|---|---|
| Processor | Any (Stripe, Adyen, Braintree, etc.) | Stripe only |
| Payment layer | AP2 (separate protocol) | Stripe SPTs (built-in) |
| Cryptographic proof | Yes (AP2 mandates) | Yes (Stripe handles) |
| Wallet support | Open wallet ecosystem | Stripe-supported wallets |
| Aspect | UCP | ACP |
|---|---|---|
| Custom capabilities | Yes (reverse-domain namespacing) | Limited |
| Extensions | Multi-parent extensions with schema composition | N/A |
| Vertical expansion | Lodging, Food announced | Commerce only |
It is possible that UCP and ACP will eventually interoperate or merge. Both solve the same fundamental problem (agents buying things from merchants) and both support MCP as a transport. If you are building today, the safest strategy is:
The UCP Proxy is a good example of this abstraction - it translates UCP to your existing store API, regardless of platform. A similar pattern could abstract UCP/ACP differences.