Sergey Bunas is Co-Founder and CTO at 21st.dev (YC W26), the largest React component registry for AI applications, used by 1.4M developers to build UI for AI-powered products.

A CS dropout and former Senior Software Engineer at Deel (YC W19), Sergey built UI systems at scale and previously launched Suggesty, an AI-powered Chrome extension that hit #1 on Product Hunt and was featured in Google's internal newsletter.

Sergey is a prolific builder who solo-built Stage, a Figma competitor with 10K users, founded Replai reaching $1K MRR in one month, and won the Cambridge AI hackathon as a solo competitor.

At 21st.dev, Sergey co-leads a platform that has grown to 200K MAU and 15,000+ GitHub stars, offering React UI components, agent templates, and an SDK for deploying frontier AI agents like Claude Code into production.

21st.dev is used by 1.4M developers globally, has become one of the top YC W26 companies by traffic, and its 21st Agents SDK is enabling a new generation of AI-native software products.