Guide Startups

ThirdLayer

Winter 2025 · Active

Building Dex, the AI Browser Copilot

Location: San Francisco, US

Founded: 2025

Team size: 2

About

ThirdLayer is an applied research and product lab building the next interface for human–AI collaboration. Our first product is Dex, an AI copilot for the browser. Think Cursor for knowledge work, optimized for speed and embedded directly where you work. Most web agents are built for set-and-forget tasks. But real work is fluid and messy—spread across tabs, tools, and evolving decisions. Dex transforms your browser into an intelligent, multimodal workspace that understands your intent through voice, text, and action. It enhances familiar interfaces, automates tedious steps, and removes the friction of handoffs. Beneath the surface, Dex is more than a browser agent — it’s a foundation for: ● Long-term, cross-modal memory grounded in real workflows ● A new interaction layer to replace static UI with a collaborative canvas ● Personalization: understanding how individuals approach tasks and navigate software We're building the infrastructure for adaptive, intent-aware systems that work the way you do.

Founders

  • Regina LinFounder

    Regina is the co-founder & CEO of Dex. She studied Mathematics with a concurrent master's in Computational Science at Harvard (dropped out). She previously co-founded Contour AI, a devOps tool for LLM evaluation, helped build the MVP an ecommerce marketplace with 40K+ customers and worked in various tech investment roles.

  • Kevin GuFounder

    Co-founder of Dex. Prev Math & Stat at Harvard, quant/ML researcher at Jump Trading, IBM Research, QuantCo, Meta.