How Rex went from zero to enterprise ready in weeks

In January 2026, Merlin Kafka and Lewis Blackwood founded Rex. Three months later, they won first place in the Vercel AI Accelerator, beating out 2,500 applicants. They also walked away with an investment from Vercel Ventures.

But the most impressive part of that timeline isn't the win. It's that from day one, Rex was ready to sell to enterprise customers at companies like Boeing, Walmart, and Volvo, the kind of organizations that ask hard questions about security before they'll even schedule a demo.

Here's how they got there.

The problem Rex is solving

Merlin and Lewis spent years before founding Rex working directly with enterprise finance teams. They saw the same problems everywhere: operational finance work is manual, tedious, and full of edge cases. It runs on legacy accounting systems, involves stacks of documents, and generates long email chains between companies and their vendors and customers.

"Up until now, you could never really automate it because it's full of edge cases and nuances," Merlin says.

Rex changes that. The company builds AI agents that run accounts receivable and accounts payable operations end to end, handling inbox triage, supplier portal management, and cash application around the clock. Their customers are enterprise finance teams led by heads of order-to-cash and finance leaders at large B2B companies.

Why they applied to the Vercel Accelerator

When Merlin and Lewis came across the Vercel AI Accelerator, the decision to apply was straightforward. They were already fans of how Vercel operates as a company and what it stands for around shipping and design quality. But there was another reason it was a clear fit.

"All the credits and the partner tools were pretty much exactly our tech stack at Rex," Merlin says. "I remember looking through the list of credit and partner tools and I thought, wow, this is literally everything we're running on, including WorkOS."

The six-week program gave them access to a cohort of 40 companies building across AI, developer tools, healthcare, and more, plus sessions with AI leaders and experts. On Demo Day in April, they pitched to a room of VCs and AI leaders and took first place, selected by Guillermo Rauch and a panel of judges from Anthropic, OpenAI, Browserbase, AWS, and Product Hunt.

Enterprise ready from day one

Selling to enterprises isn't something most early-stage startups try to do. The security reviews, procurement processes, and compliance requirements can slow everything down. Rex decided to take it on from the start, because their customers gave them no choice.

"We are essentially selling to enterprises from the get-go," Merlin says. "Security and enterprise-grade authentication was essentially critical for us, so that from day one we could basically be providing the level of security and authentication that any enterprise would expect."

That meant they needed SSO, SCIM provisioning, and directory sync working before they could close deals, not after.

How WorkOS fit in

Rex had been aware of WorkOS before the accelerator. "We kind of had always seen WorkOS on the horizon as something maybe to use one day," Merlin says. The accelerator credits made that day come sooner, and once they were building with it, the decision was clear.

They use AuthKit for authentication, Google and Okta SSO, Directory Sync for user provisioning, Magic Auth for passwordless authentication, domain verification, and custom branding. In short, the full enterprise auth stack.

What impressed them most wasn't just the feature set but how well it was built. "Everything works exactly how you'd expect it to work, and there aren't any nasty surprises along the way," Lewis says, "which hasn't always been the case with every auth platform I've used in the past."

The SCIM setup experience stood out specifically. "I remember the first time going through the SCIM workflow as a user, testing things, and I thought the guided step-by-step process was pretty slick," Merlin says. Setting up SCIM has historically meant tedious copying of credentials and records. The WorkOS flow made it feel easy.

A week to full enterprise auth

On a clean codebase with good documentation, the implementation moved fast. Initial auth with Google SSO took a matter of days. Adding enterprise SSO, SCIM, and testing took another three to four days on top of that. Total time from nothing to a fully working enterprise auth setup: roughly a week.

"Your docs are incredible," Merlin says. "If you use cloud code to get started to build some of this stuff, you can just knock it out very quickly when you have a standard implementation."

The payoff showed up almost immediately in their sales process. When a prospect asked during procurement whether Rex supported Okta and SCIM, the answer was yes, instantly, without needing to stop and build anything or delay the conversation. "It just didn't hold up the procurement process," Merlin says. "That's exactly what you want."

What they'd tell other founders

For founders thinking about going enterprise early, Merlin's advice is practical: choose your auth provider carefully and choose the right one from the start. Lewis adds something less obvious. Good design matters even when selling to enterprise.

"So many enterprises have had to deal with bad software that doesn't look great and isn't nice to use," Lewis says. "Good design and product sense, even when building for enterprise, is one thing to keep in mind." In a market full of clunky tooling, a polished product is a genuine differentiator.

What's next for Rex

Rex is now out of stealth, backed by Vercel Ventures, and building out their enterprise pipeline. The accelerator gave them the network, the tools, and the momentum. The foundation they built in those first few months, including their auth infrastructure, is what lets them move fast without compromising on the security requirements that enterprise customers demand.

Get your app enterprise ready from day one

Rex's story isn't unique in one respect: most startups that sell to enterprises face the same early pressure. A prospect asks about Okta. A security review flags missing SCIM support. A deal stalls because SSO isn't ready yet.

WorkOS is built so that doesn't have to happen. With AuthKit, you get enterprise SSO, directory sync, passwordless authentication, and a polished admin experience out of the box, so you can ship enterprise-grade auth in days and stay focused on your core product.

Get started with WorkOS and be ready for your first enterprise customer before they ask.