Rex

Rex is an AI platform built by a small team in London and San Francisco that deploys specialized agents to run accounts receivable and order-to-cash operations for global enterprises. The company was founded by Merlin Kafka (previously CPO at Sequence, a16z-backed) and Lewis Blackwood (previously engineering lead at Sequence and early engineer at GoCardless), who spent four years building billing and AR software before starting Rex. According to the company, Rex is backed by Y Combinator (S26 batch) and was selected #1 of 2,500 teams in the Vercel AI Accelerator.

What It Is

Rex is an agentic finance platform that connects to a company's existing ERP, CRM, email, and communication tools to execute accounts receivable work end-to-end — without requiring migration or manual knowledge transfer. Rather than replacing systems of record, Rex reads from them, builds context from historical data, and runs continuous operations across collections, dispute resolution, supplier portal uploads, cash application, and inbox triage. The platform positions itself as an alternative to offshore outsourcing and transformation consulting, offering outcome- and SLA-based pricing with onboarding measured in days rather than months.

How the Agents Work

Rex agents operate across every open invoice and customer account simultaneously, handling tasks that previously required human judgment across fragmented systems:

• Inbox triage: Automatically processes and routes AR emails, with the company claiming a 90%+ auto-triage rate and a 30-minute average response time.
• Portal operations: Logs into and submits to 30+ customer supplier portals (e.g., SAP Ariba, Coupa) without manual intervention.
• Cash application: Matches incoming payments to open invoices and retrieves remittance data from vendor portals.
• Collections and dunning: Proactively follows up on overdue accounts, flags payment cadence drift, and escalates risk cases.
• Dispute capture: Extracts dispute reasons, PO numbers, and payment terms from email threads and logs them to the ERP.
• Escalation: Routes sensitive cases — such as legal hold notices — to the appropriate finance ops team member.

A live activity feed and natural-language query interface let AR managers ask questions like "Why is Samsung's payment stuck?" or "Flag accounts at risk of slipping past 60 days."

Integrations and Architecture

Rex connects to existing enterprise stacks without requiring data migration. Supported integrations include:

• ERPs: Oracle NetSuite, SAP, Microsoft Dynamics, Workday, Oracle Fusion
• CRM: Salesforce
• Communication: Slack, Microsoft Teams
• Document storage: SharePoint, Google Drive, Gmail

The company states that Rex reads years of historical context from these systems so finance teams do not need to explain processes or transfer knowledge manually.

Enterprise Security and Compliance

Rex is built for enterprise deployment with the following security posture, as stated on the company website:

• SOC 2 Type II (monitoring)
• AES-256 encryption at rest and in transit
• GDPR compliant with EU data residency
• Role-based access control and full agent audit logs
• Enterprise SSO via Okta, Azure AD, Auth0, and others, plus SCIM directory sync
• Customer data is not used to train models

Why It Got Attention

Rex won the Vercel AI Accelerator (ranked #1 of 2,500 teams) and joined Y Combinator's Summer 2026 batch. The company also published a customer story with Synthesia, describing how Synthesia moved its AR inbox, 30+ customer portals, and collections to Rex without adding headcount. Rex claims its platform reduces Days Sales Outstanding by 12 days and saves 15 hours per AR operator per week, though these figures are vendor-published and baseline-dependent. The company is also backed by angel investors from Stripe, Coinbase, McKinsey, Browserbase, Braintrust, and Cursor, and has partnerships with NVIDIA, Deloitte, and AWS.