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21st

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Infrastructure and UI building blocks for the agentic internet

Winter 2026Founded 20243 peopleSan Francisco, CA, USA
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AI insightcan contain mistakes
AI Application Component RegistryAPI/InfraDevelopers building AI agents and agentic appsMedium competition
Moat
Large developer community (370K MAU); comprehensive component library; SDK with built-in infrastructure.
Key risk
Component quality and maintenance burden; competition from cloud providers; developer fragmentation.
Why now
Agentic app development is exploding; teams need pre-built infrastructure (UI, memory, observability).
Competitors
npm, Component libraries, UI libraries (React, Vue), cloud provider SDKs
โ†ป Pivot / rename signal

This company has previously operated under โ€œ21stโ€, โ€œ1code by 21st.devโ€, โ€œ1code (21st.dev)โ€, โ€œ1code (ex: 21st.dev)โ€, โ€œ1code (21st.dev)โ€, โ€œ21st.devโ€. A rename frequently marks a pivot in positioning or product โ€” useful raw material for variant ideas.

About

21st.dev is the largest React component registry for AI applications, used by 2M developers (370K MAU). We provide the building blocks to create AI agents and agent-powered apps: UI components, agent templates, and an SDK with built-in UI, tools, memory, observability, and managed infrastructure.

Founders ยท 2

Serafim Korablev
Serafim KorablevCEO / co-founder

One of the first full-time vibe-coders (since October 2023). Co-founder of 21st.dev, a UI components registry with over 1m users. Previously co-founded Rork.com (then a web app builder for Next.js), the first Telegram-native memecoin launchpad (multi-million exit), and Via, a cross-chain crypto routing protocol with $1.5B GTV backed by Naval, Safe, Sandeep, and others. Passionate about design and basketball.

Sergey Bunas
Sergey BunasFounder
Google๐ŸŽ“ Cambridge

CS dropout. Senior Software Engineer at Deel (W19). Built Perplexity before Perplexity (Suggesty, 2022 โ€” #1 Product Hunt, featured in Google's internal newsletter). Solo-built a Figma competitor pre-AI (Stage, 10K users). Cambridge AI hackathon winner (solo)

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