Rex — AI Operations Partner for Enterprise Order-to-Cash

Rex builds an AI-native service that deploys specialized agents to manage enterprise order-to-cash operations, continuously handling invoices, customer accounts, and exceptions at scale. Founded in 2026 and based in London, the company is backed by Y Combinator (Summer 2026) and won the Vercel AI Accelerator.

• Founded: 2026
• HQ: London, United Kingdom
• Sector: AI Agents / Enterprise Finance Operations
• Funding Stage: Y Combinator Seed (Summer 2026)
• Notable Backers: Y Combinator, Vercel

Core Data Grid

Rex Leadership & Structural Breakdown

• Key Leadership: Merlin Kafka (Co-Founder & CEO) and Lewis Blackwood (Co-Founder & CTO). The founders previously built Sequence, an a16z-backed finance operations platform that reached Series A. Lewis Blackwood had early experience at GoCardless (YC S11).

• Primary Competitors: Vic.ai, AppZen, HighRadius
• Core Use Cases & Market Problem: Global enterprises with complex, high-volume order-to-cash processes that still rely heavily on manual work for invoice management, collections, and exception handling. The platform targets the persistent operational drag in accounts receivable that slows cash conversion and increases cost.

Explanation

Rex uses AI agents to run the day-to-day work of order-to-cash teams. Instead of humans chasing invoices or manually resolving disputes, the system continuously monitors accounts, flags and resolves exceptions, maintains audit trails, and operates under enterprise controls and SLAs.

Target Customers & Adoption Context

Large enterprises and organizations with significant accounts receivable volume that currently outsource or staff heavily for order-to-cash operations. It appeals to finance leaders seeking to reduce headcount dependency while maintaining or improving control, compliance, and cash flow predictability.

Capital & Traction Signals

Y Combinator Summer 2026 backing combined with winning the Vercel AI Accelerator (selected from 2,500 applicants) provides early external validation. The founding team brings direct prior experience scaling a finance operations platform to Series A with a16z. The company emphasizes outcome-based pricing and enterprise-grade features such as approval controls and full audit trails.

Editorial Assessment (Investor Lens)

Rex targets the application of agentic AI to one of the most manual and costly back-office functions in large enterprises. The order-to-cash process remains stubbornly people-intensive even as front-office AI adoption accelerates, creating a clear efficiency opportunity. The founders’ track record building and scaling Sequence to Series A with a16z supplies credible domain expertise, while the Vercel AI Accelerator win adds a high-signal technical and market validation. Momentum will likely depend on enterprise sales execution and depth of integration with major ERP and CRM systems. Key watchpoints include data security and compliance requirements in finance workflows, as well as the typical length of enterprise AI deployment cycles. The combination of experienced founders and timely positioning in the agentic operations layer offers asymmetric potential if Rex can demonstrate measurable cash acceleration and cost reduction at scale.

Last Updated: June 2026

Sources

• rex.inc (company site and blog)
• Y Combinator company page
• Vercel AI Accelerator announcement
• Founder background references (Sequence, GoCardless)