For a chat runtime, start with assistant-ui (MIT, React primitives plus a free set of Elements), CopilotKit (MIT, a frontend stack with human-in-the-loop hooks) or shadcn/ui's AI Elements (copy-in patterns, no package). For finished agent moments such as approval cards, run timelines and tool call rows, several libraries sell them as shadcn-installable source: Arc, affectUI, React Bits Pro, HextaUI, BoardUI, ReUI and PixilUI among them. This page lists what each site says, unranked.
How this list was made#
Every row was read on the library's own site or GitHub repository on 4 November 2026; the sources are listed below. Prices are as the site printed them that day. Where a site did not answer an automated read, or a fact was not on the pages read, the table says "not read" rather than guessing. PixilUI is one of the libraries listed, so the rows stick to what each site says about itself, and no list is ranked.
Chat runtimes and free foundations#
| Library | What it is, in its own words | License or price | Install |
|---|---|---|---|
| assistant-ui | "React components for AI chat interfaces"; primitives for React, Vue, React Native and the terminal, plus Elements such as an approval card, permission grant, reviewable diff and trace waterfall | Library free under MIT; optional Assistant Cloud: Free (200 MAU), Pro $50 a month (500 MAU), Enterprise custom | npm runtime, shadcn registry |
| CopilotKit | "The frontend stack where agents meet users", connected to agent frameworks through AG-UI; docs cover chat, generative UI and human-in-the-loop | MIT on GitHub; hosted pay as you go from $49 a month (10,000 interactions included) | npm |
| AI Elements in shadcn/ui | "Patterns for agentic interfaces, built from shadcn/ui components": Chat, Message, Reasoning, Tool, Plan, Confirmation, Queue, Subagent and more | Free; "There is no package to install. The code is yours." | shadcn CLI |
| AI Elements (elements.ai-sdk.dev) | Vercel's component library for the AI SDK; its banner says it is moving to shadcn/ui and "will be deprecated at the end of November 2026" | Free | npx ai-elements or shadcn CLI |
| prompt-kit | "Customizable, high-quality UI components for AI applications", built on shadcn/ui | MIT on GitHub | shadcn CLI |
Libraries that sell agent moments#
| Library | What it is, in its own words | Price as listed | Free tier |
|---|---|---|---|
| Arc | React components and blocks "designed for AI-assisted frontend development"; 239 components and 139 blocks | Pro $149 a year or $249 once; team $799 once or $449 a year | 121 components and 22 blocks, MIT |
| affectUI | "Agent-ready React UI for AI products and SaaS"; 131 items, each one .tsx file with styles inside, no Tailwind | Individual $199 once; Team $499 once | 40 items, MIT |
| React Bits Pro | 230 animated components, 300 page blocks, 300 application UI blocks, 15 templates and an AI Agent Kit | Starter $129, Pro $249, Ultimate $349 once; or $79, $149, $199 a year | reactbits.dev, separate |
| HextaUI | shadcn/ui blocks "with streaming, tool calls, voice and agent states already handled" | Solo $49 once until 30 November 2026, then $79; Team $149, then $249 | 65 components, MIT |
| BoardUI | "A React + Tailwind CSS v4 design system for dashboards and agentic interfaces"; Pro adds chart cards, agent components and templates | €149 once with a year of updates; €199 lifetime | Free components and blocks |
| ReUI | "A first-class shadcn registry": 1,264 free examples, 672 premium blocks, every component in Base UI and Radix | Not read: prices are on its pricing page | Free primitives and examples |
| beUI Pro | "Premium animated React blocks and complete Next.js landing-page templates", with an agents category | Not read today | beui.dev |
| Kobra | "A React component library for shadcn", 90 names, 11 free | Not read today | 11 components |
| AI SDK Agents | Not read: the site refused an automated read on 4 November 2026 (HTTP 429) | Not read | Not read |
| PixilUI | Approval card, run timeline, tool call row, streaming text and thinking state as source you own, one foundation in two design styles | Pricing | Free items, MIT |
Counts are each library's own and measure different things (components, blocks, examples, variants), so they do not compare across rows.
How to choose#
- You need the chat itself. Thread list, composer, message list, persistence: take a chat runtime (assistant-ui, CopilotKit, AI Elements) and keep it.
- You need the moments around the chat. An approval with risk and a receipt, a run that reads like steps, tool calls you can open: take them from a library that ships them as source, next to the runtime. Most install with the shadcn CLI into their own folder, so two can sit in one app.
- Your agent writes the code. Look for an MCP server,
llms.txtand per-item markdown; every paid library above lists at least one of these. See UI components for Claude Code and Cursor for PixilUI's setup. - You care how it looks. Open the demos; read whether the states you need (pending, error, empty, reduced motion) are shown. Listings rarely say.
Questions#
What is the best React library for AI chat?
It depends on the job. For a chat runtime with threads and a composer, assistant-ui, CopilotKit and AI Elements are the common starting points, each free. For agent moments such as approvals and run timelines, several libraries sell finished components; compare their demos and states rather than counts.
Is Vercel AI Elements deprecated?
Its site says AI Elements is moving to shadcn/ui and the standalone project will be deprecated at the end of November 2026. New projects should install AI Elements from shadcn/ui; installed components are source in your repo and keep working.
Can I use two of these libraries in one app?
Usually. Libraries that install through the shadcn CLI write source into their own folders, so a chat runtime and an agent-moment library can sit side by side. Keep one set of tokens per surface so a screen does not mix two looks.
Are any of these libraries free?
assistant-ui, CopilotKit, prompt-kit and AI Elements are free, and most paid libraries above also publish a free tier under MIT.
Related#
- Why AI-built apps look the same, and what to change: why installing finished parts beats prompting each one.
- Is AI-generated UI accessible? What the studies found: what to check in any library's demos.
- Human approval with the Vercel AI SDK: one agent moment, wired.
Sources#
- assistant-ui llms.txt and pricing, read 4 November 2026
- CopilotKit docs llms.txt, read 4 November 2026
- CopilotKit pricing, read 4 November 2026
- shadcn/ui: AI Elements, read 4 November 2026
- AI Elements, read 4 November 2026
- prompt-kit llms.txt, read 4 November 2026
- GitHub repositories of assistant-ui, CopilotKit and prompt-kit (license field), read 4 November 2026
- Arc llms.txt, read 4 November 2026
- affectUI llms.txt and pricing, read 4 November 2026
- React Bits Pro llms.txt, read 4 November 2026
- HextaUI llms.txt, read 4 November 2026
- BoardUI llms.txt and pricing, read 4 November 2026
- ReUI llms.txt, read 4 November 2026
- beUI Pro llms.txt, read 4 November 2026
- Kobra llms.txt, read 4 November 2026
- AI SDK Agents pricing (returned HTTP 429 to the read), read 4 November 2026