tl;dr: We make it stupid easy to deploy frontier AI agents (Claude Code, Codex, others) inside your product. Define your agent in TypeScript, deploy with one command, ship it to your users.

https://youtu.be/1WcdHbyik18

How we got here

Last year we built 21st.dev - a React component registry that 1.4M developers use to build UI for AI apps.

We also built our own AI agents from scratch to power the product. All custom. 15,000+ GitHub stars.

Then Claude Code arrived. We rewrote our agents on top of it - and they got better overnight than in months of our own work. That was a humbling moment.

But here's the thing - getting Claude Code into production was brutal. These agents aren't API calls. They're runtimes. They rely on bash, filesystem, persistent sandboxes. So you can't just run them on Vercel (timeouts, no fs). Then the questions start piling up. How do you sandbox securely? How do you make sure your env vars aren't stolen from the sandbox? How do you handle streaming? Billing? Observability? You end up building way more infrastructure than you planned for.

We spent 2 months deep in these problems. And then we realized - every team building on frontier agent SDKs is facing the exact same wall we just climbed over.

So we turned our infrastructure into a product.

21st Agents SDK

The agent SDKs give you the brain. We give you everything else.

What you get out of the box:

• Sandboxed code execution (powered by E2B) - secure, persistent
• Credential security - proxy layer so your keys never touch the sandbox
• SSE streaming, compatible with AI SDK
• Crafted agent chat UI with themes
• Usage limits & billing
• Observability

How it works: you define your agent in code - custom tools, hooks like onFinish, sandbox configuration (which files, which CLI tools, which tokens). Then you deploy with our CLI. And you have a hosted agent you can manage via API. It's AI SDK compatible so you can just plug and play on the client side.

SDK supports React, Next.js, Node, and Python.

Why this matters now

The best agents aren't being built from scratch anymore. They're being built on top of frontier agent runtimes from Anthropic, OpenAI, and others. But shipping them to real users? That's still a mess. The gap between "agent works on my machine" and "agent works for my customers" is enormous.

We already closed that gap for ourselves. Now we're the infra layer so you don't have to.

Try it

https://21st.dev/agents

If you're building with frontier AI agents and hitting production walls - we want to hear about it. DM us on X (@serafimcloud, @sergeybunas) or email founders@21st.dev