assistant-ui

This project is an open source TypeScript and React library for building the frontend of AI chat products and agents. It supplies composable primitives and a runtime that owns the conversation thread, the response stream and tool calls, so a team can put a production chat interface in front of whatever backend already runs its model. A single init command scaffolds a working thread, and the CLI copies the UI source into the project so every surface can be reshaped. It is aimed at developers shipping AI features in web, native and terminal apps; the same chat model runs on React, React Native and Ink. Adapters connect it to the Vercel AI SDK, LangGraph, LangChain, Mastra or a custom backend without rewriting the UI. The runtime handles streaming, reasoning display, tools, human approval, sources, attachments, message branching, suggestions, voice and generative UI. An optional hosted service, assistant cloud, adds thread persistence, thread lists, automatic titles and user or workspace scoped history with Clerk, Auth0, Supabase, Firebase or a custom auth provider. The library is free under the MIT license, including for commercial use. assistant cloud is priced by monthly active users, counted as users who send at least one message: Free is $0 with 200 MAU included; Pro is $50 per month with 500 MAU included and $0.10 per additional MAU, plus early access to new features; Enterprise is custom and adds a custom backend integration, data replication, dedicated support, a 99.99% uptime SLA and on premises deployment. The published plans are sized for B2B products, and consumer apps are quoted separately. Cloud is entirely optional: teams can keep their own database and persist threads themselves without ever opening an account.