Rex

Rex (rex.inc) is an AI-native order-to-cash service that deploys AI agents to run finance operations end to end, including collections, reconciliation, and customer portal uploads. It connects to a company's existing stack without requiring migration and continuously manages invoices, customers, and exceptions, replacing people-heavy accounts-receivable operations. Rex says it is live with pre-IPO tech companies and manages over $500M in receivables from Fortune 100 customers, cutting manual follow-up cycles from weeks to hours, and it was named the top winner of the Vercel AI Accelerator out of 2,500 teams. The company was founded in 2026 by Merlin Kafka (CEO, former CPO at Sequence) and Lewis Blackwood (CTO, former founding engineer at Sequence and early team at GoCardless), and is part of Y Combinator's Summer 2026 (S26) batch.