21st
Infrastructure and UI building blocks for the agentic internet
About the Company
21st.dev is building the production layer for frontier AI agents.
Agent SDKs from Anthropic, OpenAI, and others give you the brain — we give you everything else: sandboxing, auth, UI, streaming, billing, and observability. Think Railway or Vercel, but for agents.
Our internal pitch: "Claude Code SDK is React. We're building Next.js."
Our unfair advantage is community. 1.8M+ developers have built with us, 370K are active monthly, and we've earned 15,000+ GitHub stars. Community is how we earn trust with builders — and how we learn exactly what breaks when teams try to ship agents to real users. Revenue comes from the companies those developers work at.
Public Beta launched March 2026 (YC W26). Backed by Y Combinator, Gokul Rajaram, Christian Reber (Wunderlist, Pitch), Thomas Wolf (Hugging Face), Nick Baumann (OpenAI Codex), and Andy Zhang (Google DeepMind). Consistent weekly deploy growth since launch.
How we work: in person in SF, Monday–Friday. Small, sharp, low-ego team. High standards, high velocity.
We believe the 21st-century internet will be built out of agent-native building blocks. We want to be where those blocks live — and where the infrastructure to ship them to end users runs.
Tech Stack
The problem we solve: getting Claude Code, Codex, or OpenCode into production isn't an API call — it's a runtime. Sandboxes, proxies, streaming, billing, observability. Teams spend two months building infrastructure before a single customer sees their agent. We turned that infrastructure into a product.
What we ship:
- Sandboxed runtimes — isolated execution environments for agent code
- Credential proxying — agents call third-party APIs without ever touching user secrets
- Sub-agent orchestration — spawn, supervise, and compose agents at runtime
- SSE streaming — token-by-token UX primitives for agent output
- Auth, billing, observability — the non-model plumbing every agent product needs
- VPC deploy + Scale tier — on-prem, SSO, audit logs, budget caps for enterprise
What we've built before: Magic MCP, 1Code (5k GitHub stars), and the SDK powering 21st Agents today.
How we work on the engineering side: ship fast, measure deploys weekly, treat the developer community as the primary feedback loop. If it breaks for a team trying to put an agent in production, we want to know before their Slack does.
Founders
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.
Open Positions at 21st (1 Jobs)
Ready to start your space career at 21st?
