Columbia MBA Founder Takes AI Legal Tech Startup Regbase To Y Combinator

Among the fundamental principles of entrepreneurship are finding an overlooked problem, building a solution, and moving quickly when opportunity appears. 

Working as an ESG researcher for the prestigious law firm Paul, Weiss, Natalie Aresta-Katz tracked environmental, social, and governance disclosure laws across more than 90 countries, coordinating local law firms and a team of as many as 13 paralegals. The work was painstaking, repetitive, and still prone to missed regulations and human error. 

To stay up to date, she needed to run Google searches in 45 languages every month. She just knew there had to be a better way.  

Aresta-Katz, a Class of 2026 MBA from Columbia Business School, is co-founder of Regbase, an AI-native legal research platform that helps companies, law firms, researchers, and government vendors track new and proposed laws across countries, languages, and jurisdictions. Those include regulations buried on obscure government websites, consultation portals, social media pages, and other sources that traditional search engines and large language models may never index. 

Regbase was accepted into Y Combinator’s Spring 2026 batch, making Aresta-Katz the first current CBS student admitted to the accelerator since 2019. She was also one of just 18 women among the batch’s 431 founders, perhaps one of the biggest surprises of her journey so far.  

“I didn’t realize that the gender ratio at YC (and in AI more broadly) is actually getting worse, not better,” she tells Poets&Quants. 

“During partner conversations I sometimes felt like I was speaking for every woman in the batch. I decided to do a Women of YC series and feature each of my batchmates on LinkedIn to share their stories and encourage more women to apply.” 

Aresta-Katz built Regbase with co-founder Ethan Shea, a former staff engineer at Vercel with expertise in agentic infrastructure and security. The company completed Y Combinator’s three-month program this summer and closed an undisclosed seed round following Demo Day. 

The company has already uncovered regulations posted only on LinkedIn, Facebook, or X; identified 80 greenhouse-gas disclosure requirements across 45 countries for a global manufacturer; and found $400 million in expiring school-safety grants for a client selling protective equipment, according to the YC launch page.  

Aresta-Katz began building Regbase shortly before enrolling at Columbia Business School, where she watched generative AI evolve from a novelty into what she calls a game changer. She folded the startup into her MBA experience wherever she could, using it for class projects, slipping out of lectures for client meetings, hiring a small team, and winning business from major law firms. 

Aresta-Katz recently shared her experience with Poets&Quants. In the exchange below, she talks about how CBS faculty urged her to apply to Y-Combinator, building a company while earning an MBA,  and why business school may be one of the safest places to take a serious risk. 

What was your reaction when you found out Regbase had been accepted into Y Combinator’s Spring 2026 batch? 

At first it was really just shock. I had just finished the training for a program called REAP where you teach an entrepreneurship course at a New York State prison. My first reaction was that I really hoped I could still participate. Thankfully they let me participate before I left for YC!  

How did CBS factor into your path to Y Combinator, and what role did the MBA play in helping you build Regbase? 

I was talking to a CBS professor, Mattan Griffel, who previously did YC twice, about my company and he suggested I just submit an application and not overthink it. Until then I had been bootstrapping and growing through revenue, so the world of venture capital was very new to me.  

I started building my company right before coming to CBS, and got to watch AI evolve from a novelty to a gamechanger during my MBA. It was inspiring to meet current founders that came to speak on campus. When I became co-president of the Columbia Entrepreneurs Organization (CEO), I tried to bring as many founders to campus as possible, from all kinds of companies. 

You said you are the first CBS student accepted to YC since 2019. What has the response been like from classmates, faculty or the broader CBS community? 

My classmates were extremely supportive! My co-presidents at Columbia Entrepreneurs Organization (CEO) even threw a goodbye party. I initially told the school I was going to be dropping out, but a few professors forgave my absences, and the administration let me take independent study so I could still get my degree.  

Take us back to the origin of Regbase. What were you seeing at Paul, Weiss that made you think, “There has to be a better way to do this”? 

Me and a team of up to 13 paralegals were doing manual research about ESG disclosure laws all around the world. It was extremely hard, even when we hired local lawyers, because everyone made mistakes and missed relevant laws. AI made mistakes and missed things too, but it was catching sources that nobody else could find, so I thought there might soon be a way to fully automate my job along with the attorneys overseeing the process. 

Your website says many important legal updates are not indexed by search engines or picked up by LLMs. What kinds of places do these rules actually appear, and what is one of the strangest or most surprising places Regbase has found one? 

There was a proposed law “open for commentary” that was hidden behind a QR code. You had to scan it with your phone and watch a thirty-second ad before you could read the document, and only on your mobile device.  

How does Regbase work at a high level? What are the typical use cases? 

We track global regulations (existing and proposed) to help companies comply and prepare for new requirements. Internal compliance and policy teams, as well as law firms use us to stay on top of new laws and implement changes, automatically.  

There’s a lot of discussion right now about AI hallucinations in legal work. How do you build trust and accuracy into a tool that is searching legal and regulatory sources? 

We map everything back to the original government document. Almost all hallucinations happen because some data or context is missing. Finding all of the sources is our specialty, and having the source documents prevents that issue. 

During your MBA, you acquired Big Law clients, hired a small team and got accepted to YC right before your final semester. How did you balance building the company with being a full-time student? 

I think the truth at business school is that everyone has something else going on, especially in New York. I slipped out of classes to take meetings and tried to work my company into my actual course work. If we needed an example company to present on, we used Regbase.   

You’ve mentioned that you are one of 18 women out of 431 people in the current YC batch. What does that mean to you, and has it shaped the way you think about this opportunity? 

I didn’t realize that the gender ratio at YC (and in AI more broadly) is actually getting worse, not better. During partner conversations I sometimes felt like I was speaking for every woman in the batch. I decided to do a Women of YC series and feature each of my batchmates on LinkedIn to share their stories and encourage more women to apply. 

What has the YC experience been like so far, especially while you are also finishing an MBA? 

It has been exciting and exhausting! Thankfully I only had two assignments to submit during the batch.  

We just completed the batch. We spent three months doing nothing but building our company, learning from experienced entrepreneurs, and getting clients. It’s an intense program but you make a lot of progress!  

What has been the hardest part of building Regbase so far, and what has surprised you most about selling to law firms, regulated companies or government vendors? 

Sometimes all it takes to sell to a law firm is their client insisting. We have had law firms refer us to clients, and clients refer us to law firms. This flywheel effect was a pleasant surprise.  

What does success look like for Regbase over the next year?  

We are going to keep expanding and serving more companies across industries. We will build a team and operationalize so that we can scale. 

What advice would you give to MBA students who are building companies while still in school? 

Give it your all! For many students, this is the least busy they will ever be in their careers. It’s worth trying something new, especially since MBAs are a low-risk environment. The worst thing that can happen is you fail and try again! 

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