UCP vs ACP in 2026: A Technical Comparison of AI Commerce Protocols

TL;DR Two protocols now power AI shopping. Google's UCP (Universal Commerce Protocol) and OpenAI's ACP (Agent Commerce Protocol) take fundamentally different approaches to the same problem: how do AI agents discover, browse, and buy products on behalf of users? Here is the side-by-side comparison: Dimension UCP ACP Created by Google + Shopify OpenAI + Stripe Announced January 2026 (NRF) February 2026 Architecture Decentralized (merchant-hosted) Centralized (platform-controlled) Discovery /.well-known/ucp JSON on your domain OpenAI product catalog Payment processor Merchant's choice (Google Pay, Stripe, Shop Pay, custom) Stripe only Transaction fees Payment processor fees only 4% OpenAI + ~2.9% Stripe + $0.30 Total cost per $100 sale ~$3.20 (Stripe) ~$7.20 (OpenAI + Stripe) Profile control Merchant owns and hosts Platform controls listing Protocol compatibility A2A, AP2, MCP, REST Standalone (open-sourced) Signing/auth Ed25519/ES256 JWK keys Stripe API keys Partners 20+ (Etsy, Target, W