21st

The official 21st SDK for Go is here! Manage AI agent sandboxes, threads, and tokens — straight from your Go backend. Here’s how to get started 🧵

@21st_dev × @agentmail New template to build Claude-powered agents with real email access - out of the box.

Nia now integrates with @21st_dev (YC W26): chat with any GitHub repo using 21st Agents SDK. Index a repo, spin up a sandboxed agent, and get answers grounded in the full codebase.

Someone made a YC W26 tier list. 21st ended up in S tier. Appreciate the vote of confidence. Back to building.

🎉 New Investment: @21st_dev 🎉 Excited to share that I’m investing in 21st alongside @YCombinator. 21st is building infrastructure and UI building blocks for the agentic internet. Their platform is already used by over a million developers building AI-native products, providing reusable components, templates, and tooling specifically designed for AI applications and agents. Their newest product, the 21st Agents SDK, makes it dramatically easier for developers to embed production-ready AI agents directly into their applications. Instead of building complex infrastructure from scratch, developers can define an agent in a few lines of TypeScript and deploy it instantly. The SDK includes built-in chat UI, sandboxed execution environments, tool integration, streaming responses, cost tracking, and observability — all the infrastructure required to run real AI agents in production. One exciting use case is integrating Claude Code–powered agents directly into products. With the 21st Agents SDK, teams can quickly add powerful agent capabilities to their apps without building the underlying agent runtime themselves, enabling a new generation of AI-native software. The company is founded by @serafimcloud and @sergeybunas, two builders deeply embedded in the developer ecosystem. Serafim previously built widely used developer products and crypto infrastructure, while Sergey built UI systems at Deel and has repeatedly launched developer tools that gained strong early traction. Their product taste and speed are clear in what they’ve already shipped. Excited to support them as they build core infrastructure for the next wave of AI applications.

We're launching 21st Agents in beta. It's the infrastructure layer for Claude Agent SDK - runtime, sandboxing, billing, UI, streaming - so you can ship agents to production without building infra from scratch. Think Vercel for Claude Agent SDK. Full walkthrough in the video below 👇

21st Agents SDK is live on Product Hunt 🔥🔥 producthunt.com/posts/21st-age…

We’re building Next.js for frontier agents!

We shipped an Email Agent template. Your AI agent gets its own inbox — send outreach, read responses, auto-reply. All through chat. Built on @21st_dev Agents + @agentmail

If you like UI components, you’re going to like our Agent Theme Builder

Agents SDK by @21st_dev comes with beautiful theme presets and a full theme builder Add an AI agent to your app, fully styled to match your product, in minutes. Play with it here - 21st.dev/agents/theme-b…

Deploy a Claude Code-powered AI agent in 5 minutes

21st Agents is now in Public Beta. The infra layer to ship Claude Code & Codex agents inside your product. In minutes. Comment for free credits to try 🧵

File tree is now available on 1code

Codex + Sonnet 4.6 are now supported in 1code. The best UI to run and manage your agents. Download - 1code.dev

As many of you still love Magic Chat, I decided to update its UI over the weekend, as we haven't updated it for 10 months

New feature: flexible terminal layout. Dock it on the right or at the bottom.

This was the most annoying missing piece. File preview. File search. Finally shipped. All inside the best client for working with Claude Code.

1Code Automation is Claude Code, but event driven. New PR? New Linear task? Claude runs automatically in the cloud, completes the task end to end and sends you the output. No babysitting. No local setup. Just results.