AI SDK v4 (legacy)

Reference for projects still on AI SDK v4. New projects should use v6.

AI SDK v4 is a legacy version. New projects should use AI SDK v6. v4 integrations use the older @assistant-ui/react-data-stream package, not @assistant-ui/react-ai-sdk.

Why legacy

Vercel ships AI SDK majors roughly yearly; v4 is two majors behind v6. The current @assistant-ui/react-ai-sdk package targets v6+ exclusively, so v4 users plug into @assistant-ui/react-data-stream instead — the same data stream protocol that v4's toDataStreamResponse() emits.

This page is reference for existing v4 projects. Plan to migrate to v6 when feasible.

Setup

Install

npm install @assistant-ui/react @assistant-ui/react-data-stream ai@^4

Backend route

@/app/api/chat/route.ts

import { streamText } from "ai";
import { openai } from "@ai-sdk/openai";

export async function POST(req: Request) {
  const { messages } = await req.json();
  const result = streamText({ model: openai("gpt-5.4-nano"), messages });
  return result.toDataStreamResponse();
}

Frontend

@/app/page.tsx

"use client";

import { AssistantRuntimeProvider } from "@assistant-ui/react";
import { useDataStreamRuntime } from "@assistant-ui/react-data-stream";
import { Thread } from "@/components/assistant-ui/thread";

export default function Home() {
  const runtime = useDataStreamRuntime({
    api: "/api/chat",
    protocol: "data-stream",
  });
  return (
    <AssistantRuntimeProvider runtime={runtime}>
      <div className="h-full">
        <Thread />
      </div>
    </AssistantRuntimeProvider>
  );
}

AI SDK v4's toDataStreamResponse() emits the data stream wire format, so protocol: "data-stream" is required to pair with it; the default protocol: "ui-message-stream" expects the SSE format introduced in AI SDK v6.

useDataStreamRuntime accepts api, initialMessages, onFinish, onError, headers, body, and the standard LocalRuntimeOptions. For the full reference, see Data Stream Protocol.

Differences from v6

Feature	v4	v6
`ai` package	`ai@^4`	`ai@^6`
Runtime package	`@assistant-ui/react-data-stream`	`@assistant-ui/react-ai-sdk`
Runtime hook	`useDataStreamRuntime`	`useChatRuntime`
Response	`toDataStreamResponse()`	`toUIMessageStreamResponse()`
Tool schema	`parameters: z.object({...})`	`inputSchema: zodSchema(z.object({...}))`
Message type	(untyped)	`UIMessage`

Migration to v6

When you are ready to upgrade:

Swap @assistant-ui/react-data-stream for @assistant-ui/react-ai-sdk.
Update your backend to AI SDK v6's streamText (see v6 docs).
Switch the runtime hook from useDataStreamRuntime to useChatRuntime.

AI SDK provides codemods at ai-sdk.dev/docs/migration-guides that handle the package-side rewrites.

Alternative: [email protected]

An older release line of @assistant-ui/react-ai-sdk (0.1.10) supported AI SDK v4 directly. It is no longer maintained and has no upgrade path; if you are starting a new v4 project, use @assistant-ui/react-data-stream instead.

AI SDK v6Current integration; what new projects should target.Data Stream ProtocolThe runtime v4 integrations are built on.AI SDK v5 (legacy)The intermediate legacy version.