First Demo Implementation of OpenAI's Agentic Commerce Protocol (github.com)

OpenAI released the Agentic Commerce Protocol (ACP), an open standard that formalizes how LLM-driven agents transact with external vendors and payment providers. Locus (YC F25) published the first working demo sandbox implementing ACP end-to-end (Client, Merchant, PSP) so developers can experiment now. The repo (Node.js 20+, Docker Compose) spins up PostgreSQL, a Merchant API (port 4001), a PSP API (4000), an MCP server (3112) and a chat client (3000) that uses an MCP-UI-compatible Scira fork. All transactions are mocked, but the demo follows ACP endpoints and flows precisely, letting you add items, update checkout sessions (POST /checkout_sessions and POST /checkout_sessions/{id}), cancel sessions, fetch products, and complete delegated checkouts. Technically, ACP standardizes three modular roles—Client (LLM UI), Merchant (checkout session management), and PSP (vaulting credentials and minting Shared Payment Tokens)—so agents can programmatically pay without brittle RPA or exposing merchants to raw card data/PCI scope. The demo implements the Delegated Checkout: the PSP vaults payment credentials and returns a token to the Client, which posts /checkout_sessions/:id/complete; the Merchant redeems the token with the PSP to execute payment. The repo also demonstrates product ingestion (GET /products → lightweight vector store) and adheres to ACP headers, idempotency, and response formats. ACP is still draft, but this sandbox accelerates experimentation and cross-vendor agent commerce development.