Founding AI Engineer (Enterprise Finance Operations)

Apply on YC · Original job listing

• Role: Engineering / AI engineer
• Experience: 1+ years
• Visa: US citizenship/visa not required

AI Transformation for Enterprise Finance

Rex builds AI agents for enterprise finance, starting with order to cash. Our customers delegate a process to us, and we run it with agents while finance experts oversee the work. Our agents operate across email, ERPs and customer portals to resolve payment blockers and help businesses get paid.

We’re building agents that can take responsibility for complex financial workflows: reason over messy data, handle exceptions and improve through feedback from finance experts. The challenge is earning the trust to act autonomously in operations that affect real money.

Who we are

Rex was founded in 2026 by Merlin Kafka (CEO) and Lewis Blackwood (CTO). 

Merlin previously served as CPO at Sequence (a16z) and PM at Tessian (Sequoia), and studied industrial engineering at Cambridge. Lewis previously led engineering at Sequence, joined GoCardless early and founded a startup backed by GFC. He studied economics at Cambridge.

Our team brings years of experience building AI and finance products and working with hundreds of finance teams. We know this domain inside-out.

Rex is global from day one and operates across San Francisco and London.

What you’ll do

This is a generalist role and you will be immediately responsible for large product areas and new initiatives. You’ll build products end to end, from understanding a customer’s finance workflow to shipping agents that carry it out. Your work will span the agents, the financial context they reason over, and the tools finance teams use to oversee them. You’ll also build the infrastructure, evaluations and feedback loops that help agents improve from real work. You will ship to production on your first day.