CROSS-CATEGORY: The Agentic-Commerce Protocol War Breaks Open — Square/Google UCP vs OpenAI/Stripe ACP vs Shopify Agentic Storefronts
Multiple Sources·high signal
Within days three competing agent-checkout standards are live: Square + Google's Universal Commerce Protocol (July 1), OpenAI + Stripe's Agentic Commerce Protocol powering Instant Checkout for 1M+ Shopify and Etsy merchants, and Shopify's Agentic Storefronts syndicating products to ChatGPT, Google AI Mode, Copilot and Perplexity by default. Transaction fees are collapsing to standard processing rates while the agent — not a storefront — picks the merchant. The same signal is hitting payments, e-commerce platforms and POS simultaneously: the checkout/marketplace SaaS category is being rewritten as a protocol.