streaming

Original：🇺🇸 English

Translated

Guide for assistant-stream package and streaming protocols. Use when implementing streaming backends, custom protocols, or debugging stream issues.

8installs

Sourceassistant-ui/skills

Added on2026-02-04

NPX Install

npx skill4agent add assistant-ui/skills streaming

SKILL.md Content

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assistant-ui Streaming

Always consult assistant-ui.com/llms.txt for latest API.

The

assistant-stream

package handles streaming from AI backends.

References

./references/data-stream.md -- AI SDK data stream format
./references/assistant-transport.md -- Native assistant-ui format
./references/encoders.md -- Encoders and decoders

When to Use

Using Vercel AI SDK?
├─ Yes → toUIMessageStreamResponse() (no assistant-stream needed)
└─ No → assistant-stream for custom backends

Installation

bash

npm install assistant-stream

Custom Streaming Response

import { createAssistantStreamResponse } from "assistant-stream";

export async function POST(req: Request) {
  return createAssistantStreamResponse(async (stream) => {
    stream.appendText("Hello ");
    stream.appendText("world!");

    // Tool call example
    const tool = stream.addToolCallPart({ toolCallId: "1", toolName: "get_weather" });
    tool.argsText.append('{"city":"NYC"}');
    tool.argsText.close();
    tool.setResponse({ result: { temperature: 22 } });

    stream.close();
  });
}

With useLocalRuntime

useLocalRuntime

expects

ChatModelRunResult

chunks. Yield content parts for streaming:

tsx

import { useLocalRuntime } from "@assistant-ui/react";

const runtime = useLocalRuntime({
  model: {
    async *run({ messages, abortSignal }) {
      const response = await fetch("/api/chat", {
        method: "POST",
        body: JSON.stringify({ messages }),
        signal: abortSignal,
      });

      const reader = response.body?.getReader();
      const decoder = new TextDecoder();
      let buffer = "";

      while (reader) {
        const { done, value } = await reader.read();
        if (done) break;

        buffer += decoder.decode(value, { stream: true });
        const parts = buffer.split("\n");
        buffer = parts.pop() ?? "";

        for (const chunk of parts.filter(Boolean)) {
          yield { content: [{ type: "text", text: chunk }] };
        }
      }
    },
  },
});

Debugging Streams

import { AssistantStream, DataStreamDecoder } from "assistant-stream";

const stream = AssistantStream.fromResponse(response, new DataStreamDecoder());
for await (const event of stream) {
  console.log("Event:", JSON.stringify(event, null, 2));
}

Stream Event Types

part-start

with

part.type

"text" | "reasoning" | "tool-call" | "source" | "file"

```
text-delta
```
with streamed text
```
result
```
with tool results
```
step-start
```
,
```
step-finish
```
,
```
message-finish
```
```
error
```
strings

Common Gotchas

Stream not updating UI

Check Content-Type is
```
text/event-stream
```
Check for CORS errors

Tool calls not rendering

```
addToolCallPart
```
needs both
```
toolCallId
```
and
```
toolName
```
Register tool UI with
```
makeAssistantToolUI
```

Partial text not showing

Use
```
text-delta
```
events for streaming