AI SDK v4 (legacy)

Reference for projects still on AI SDK v4. New projects should use v7.

AI SDK v4 is a legacy version. New projects should use AI SDK v7. 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" });
  return (
    <AssistantRuntimeProvider runtime={runtime}>
      <div className="h-full">
        <Thread />
      </div>
    </AssistantRuntimeProvider>
  );
}

AI SDK v4's toDataStreamResponse() emits the data stream wire format with the x-vercel-ai-data-stream: v1 response header, so useDataStreamRuntime detects it automatically. If a custom proxy strips or hides that header, pass protocol: "data-stream" explicitly.

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 v7

When you are ready to upgrade:

Swap @assistant-ui/react-data-stream for @assistant-ui/react-ai-sdk.
Update your backend to the current AI SDK's streamText (see v7 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 v7Current integration; what new projects should target.Data Stream ProtocolThe runtime v4 integrations are built on.AI SDK v5 (legacy)The intermediate legacy version.