Max Thilén publishes a 29-minute reference guide on the agentic commerce protocols structuring e-commerce in 2026. The starting observation is radical: customers now complete entire purchase journeys inside AI conversations, without ever visiting merchant websites. ChatGPT Instant Checkout serves 900 million weekly users.
Two protocols are competing for this infrastructure. ACP (Agentic Commerce Protocol), backed by OpenAI and Stripe, has been operational since September 2025. It imposes a 4% commission per transaction, a structured product feed, and 5 REST endpoints for checkout. The flow is entirely conversational: the user asks, the agent searches, displays a "Buy" button, and Stripe processes payment via a shared token — the agent never sees the banking data.
UCP (Universal Commerce Protocol), announced by Google in January 2026 at NRF, federates a massive coalition: Shopify, Walmart, Target, Wayfair, Visa, Mastercard, PayPal, and 20 other partners. Its architecture is more modular, with four transport options (REST, MCP, A2A, Embedded) and two checkout modes (native within the AI interface or iframe to the merchant site). Merchants declare their capabilities via a /.well-known/ucp profile.
Amazon's absence is strategically significant. Controlling 40% of US e-commerce, Amazon has chosen a proprietary path with Rufus AI (300 million users, +60% conversion), Alexa+ for voice commerce, and "Buy for Me," which allows purchasing from competitors within the Amazon app. Amazon has even blocked OpenAI's crawlers, removing 600 million products. The market thus forms a triptych: proprietary Amazon, Google UCP, OpenAI ACP.
The guide details the technical requirements of both protocols, notably product data, which becomes the primary competitive lever when paid advertising doesn't reach agents. Descriptions must serve natural-language processing, not classic SEO: describing use cases and materials rather than stacking keywords.
The attribution crisis is the major challenge: 70-90% of purchase journeys are already invisible to traditional analytics, and agentic commerce approaches 100%. The first measurable signal is an order webhook. Thilén recommends server-side tracking, incrementality testing, and AI visibility monitoring, with maturity estimated at 18-24 months.
The projections are considerable: McKinsey anticipates $3-5 trillion in global revenue by 2030. For brands, the conclusion is pragmatic: both protocols matter. ACP dominates conversational discovery, UCP will capture intentional queries via Google. Different entry points, same customer.