Add Vercel AI SDK stream adapter and message format

[ankit-thesys]

Summary

This PR adds first-class support for the Vercel AI SDK in @openuidev/react-headless, enabling developers to use OpenUI with Vercel's ai package out of the box.

What's included

• vercelAIAdapter — a new StreamProtocolAdapter that parses Vercel AI SDK's UI message stream protocol (data-stream format with 0:, 2:, 9:, a:, e: prefixed lines) and converts them into AG-UI events
• vercelAIMessageFormat — a new MessageFormat implementation that converts between AG-UI Message[] and Vercel AI SDK's ModelMessage[], supporting:
  • User, assistant, and system messages
  • Tool calls and tool results (including multi-step tool interactions)
  • File/image attachments via experimental_attachments
  • Reasoning content parts
• vercel-ai-chat example app — a full Next.js example demonstrating both a simple chat page and an agent page with tool use, using streamText from the Vercel AI SDK on the server and FullScreen + the new adapters on the client
• Comprehensive test suites — tests for both vercelAIAdapter (stream parsing, text streaming, tool calls, finish reasons, errors, multi-step) and vercelAIMessageFormat (round-trip conversions, edge cases)

Other changes

• Added ai SDK as a devDependency in react-headless (for type imports only — no runtime dependency)
• Fixed RUN_ERROR event handler to read event.message instead of event.error
• Applied lint/format fixes across react-headless and react-ui (import ordering, formatting)

How to test

1. pnpm install from the repo root
2. Run the adapter and message format tests:

   cd packages/react-headless && pnpm test

3. Try the example app:

   cd examples/vercel-ai-chat
   cp .env.local.example .env.local  # add your OpenAI API key
   pnpm dev

   • Visit http://localhost:3000 for the basic chat
   • Visit http://localhost:3000/agent for the agent with tool use

Test plan

• vercelAIAdapter unit tests pass (text streaming, tool calls, finish events, error handling, multi-step)
• vercelAIMessageFormat unit tests pass (user/assistant/system messages, tool calls, tool results, attachments, reasoning, round-trip conversions)
• Existing react-headless tests still pass
• Manual testing with the vercel-ai-chat example app against a live OpenAI API key

Made with Cursor

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Project	Deployment	Actions	Updated (UTC)
openui-docs	Ready	Preview, Comment	Mar 5, 2026 1:04pm