REX

✍️ Notes from the Editors

Wow! What a week.

Hundreds of people joined us for our fireside chats with the founders of Kalshi and Bilt. We packed our Secret Society Afterparty on Friday with some of the coolest builders in town. Along the way, we hosted a private omakase for 30 investors. Take a peek 👇

We’re ready for a restful week ahead. Expect another incredible lineup of events for both SF and LA Tech Week in October (and even more one-off events) coming very soon!

- Ethan and Arek 🦄

World's first Chief Marketing Agent

REX is an AI-native marketing agent that looks to help creators and SMBs efficiently create, run, analyze, and monitor their ads. It is designed to assist with creating ad copy, buying ad space, targeting specific customers across particular channels, and iterating on personalized ads in an automated, proactive, and 24/7 manner. The tool combines domain expertise with LLM technology to create an agentic AI that can optimize return on advertising spend, with a key focus on hyper-personalization, ad execution and fraud detection, and ecommerce optimization.

🔗 Check it out: rexd.com

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💰 Business Model

REX charges SMBs and creators $1,000 per month for access to its platform. It then determines a budget to be allocated toward marketing spend using existing data and works with the customer to generate 2x return on ad spend (ROAS) on that number. If REX is unable to generate advertising-attributed revenue twice the marketing spend, the customer does not pay REX. If REX hits the 2x goal, the customer pays 10% of its ad spend.

📈 Traction and Fundraising

• Participated in Techstars AI in Fall 2024 in Chicago

• Finishing raising a $1.5 million pre-seed round that will close on June 30

• Doubled ROAS for Ebb Ocean Club, a CPG hair care product

• Currently in private beta with 15 customers and a waitlist of 10,000 users

👫 Founding Story

Sean Gilfillan, founder and CEO of REX, has extensive experience in marketing, but actually started his career in the military as an officer and defense strategist. After 12 years in the military, he began working as a U.S. diplomat, where he did marketing for the embassy. From there, he started multiple ventures, served as a CMO at Boeing and Viasat, and founded his own marketing agency. 

From his time in the military and in marketing, Gilfillan was very quantitative in his approach to problem solving, and observed considerable self-manufactured complexity when it came to marketing, ranging from extensive intermediaries to a lack of accountability on results. Experienced in the space and frustrated, Gilfillan initially created his own advertising agency to try and better serve small businesses in their marketing efforts. 

Specifically, Gilfillan thought there needed to be transparency, candor, and accountability when it came to advertising. He believed businesses should not be surprised with additional unexpected third parties or additional process, steps, and costs; that customers should get data-backed recommendations on why their business could or could not scale; and that ad agencies should be held accountable and incentivized to deliver results. He eventually came to the concept behind REX in early 2024, through which he could combine cutting-edge AI technology with his subject matter expertise to help businesses see a clear and quantifiable investment on their ad spend. In late 2025, he participated in Techstars AI Chicago and assembled the team in early 2025

💼 Opportunities

While the team doesn’t have any open job listings, they’re always on the lookout for new talent. Reply to this email with your resume, and we’ll connect you with REX!

🔮 Our Analysis

Many founders and small businesses reach out to advertising and marketing agencies when scaling. In this critical phase, businesses are overwhelmed by many challenges, and it is imperative that capital going toward advertising brings in greater revenue. Typically, these companies will utilize a marketing agency to strategize and run campaigns.

Sean Gilfillan, CEO of REX and a marketing veteran, emphasized three aspects he believes are required in advertising: transparency, candor, and accountability. First, it should be very clear how and why advertising dollars are used. Businesses should know upfront what to expect based on data and quantitative reasoning. Gilfillan expressed that it’s better to tell a business it will likely not be able to effectively scale and grow its product ahead of time rather than burn through capital fighting an uphill battle. Lastly, marketing agencies are often paid a flat fee, a business model that doesn’t hold them accountable for failed campaigns. 

According to REX, traditional agencies charge 12-70% of ad spend, with over $10,000 minimums that price out 89% of SMBs. Even SMBs that can afford the costs are then cash-strapped with no guarantee their capital goes to good use. And while the AI wave continues to grow, AI tools like ChatGPT can write copy but fail to account for platform-specific ad mechanics like TikTok’s viral triggers or Google Performance Max’s bidding logic. 

REX aims to fill this gap. As a vertical AI agent, REX focuses on the strategy, planning, and orchestration of advertisements across more than 32 channels, such as Google, Meta, and The Trade Desk ads. 

REX’s agentic architecture gives it leverage against platform changes, like Google’s annual policy updates, while claiming to maintain a 99.8% compliance rate across $10 million in managed ad spend. This means less time troubleshooting and more time driving ROI. It also contends that SMBs using REX cut ad management hours by 94% and avoid the 37% average ad budget waste seen on self-serve platforms. Competitors are building vertical agents as well, but they are limited in scope, typically focused on a narrow slice of the ad landscape (i.e. only supporting Facebook or Google ads). Meanwhile, REX has a channel-agnostic approach, coupled with conversion tracking across dozens of networks, pushing it into platform-infrastructure territory. 

REX’s early traction is real: it boasts a 94% retention rate, 170 campaigns run, and a waitlist of over 10,000 businesses. The team’s edge lies in lived experience and empathy, having managed hundreds of millions in ad spend and seeing firsthand how SMBs get boxed out of efficient growth. With digital ad execution more fragmented and expensive, the demand for autonomous, multi-platform AI agents is only going to grow. If traditional marketing is breaking, REX may be what comes next.

📚 Further reading

• REX Aims to Disrupt Digital Advertising with AI-Driven Growth for E-Commerce Brands [The Founder’s Press]

• REX Opportunity Breakdown [REX Website]

Written by Matthew Huo

🥲 That’s all, folks

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