Rex

Rex is an AI operations layer for enterprise order-to-cash, the finance function that turns invoices into collected cash. It targets teams at large companies still doing this work by hand across email threads, PDFs, ERPs, and customer portals, where a single mismatched PO number can hold up a seven-figure invoice for months. The launch matters now because order-to-cash sits at the intersection of two shifts finance leaders are actively navigating, the push to bring outsourced back-office work in-house and the arrival of agent frameworks capable of handling the messy, exception-heavy tasks that traditional automation and ERPs never solved. The product observes how a team already handles invoices, disputes, collections, and follow-ups, then turns each workflow into an editable operating procedure that Rex executes across thousands of accounts in parallel. Humans stay in the loop through configurable guardrails and approvals, and the system improves as reviewers correct exceptions. According to the launch video, Rex is already live in production, closing collections cases in minutes that would normally take weeks of back-and-forth, with onboarding measured in weeks. Rex was founded by Merlin Kafka (CEO) and Lewis Blackwood (CTO) , who previously spent four years building order-to-cash and AR software at Sequence , with earlier stints at GoCardless and Tessian. The team is split between London and San Francisco and is backed by Y Combinator (S26), and was selected as the top team out of 2,500 in the Vercel AI Accelerator.