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21st
Winter 2026
Active
UI building blocks for the agentic internet
3 people View on YC
21st at a glance
- Y Combinator batch
- Winter 2026
- Status
- Active
- Industry
- B2B
- Team size
- 3 people
- Location
- Not recorded
- Website
- Not recorded
Every field above comes from the Y Combinator company record. Nothing is estimated.
About 21st
21st.dev is the largest React component registry for AI applications, used by 2M developers We provide the building blocks to create agent-powered apps: UI components, agent templates.