Stream text

Read assistant text as the provider sends it.

This page describes the v0 API from v0.5.1. Use v0 package builds with these examples. Make sure that the service accepts the model ID and request protocol shown below.

npm i @xsai/stream-text@0.5.1

Examples

Basic

const { textStream } = streamText({
  apiKey: env.OPENAI_API_KEY!,
  baseURL: 'https://api.openai.com/v1/',
  messages: [
    {
      content: 'You are a helpful assistant.',
      role: 'system',
    },
    {
      content: 'This is a test, so please answer'
        + '\'The quick brown fox jumps over the lazy dog.\''
        + 'and nothing else.',
      role: 'user',
    },
  ],
  model: 'gpt-4o',
})

const text: string[] = []

for await (const textPart of textStream) {
  text.push(textPart)
}

// "The quick brown fox jumps over the lazy dog."
console.log(text)

Streams and events

streamText() exposes these streams:

• textStream: text deltas only
• reasoningTextStream: reasoning deltas only, when the model emits them
• eventStream: normalized xsAI events
• fullStream: parsed chat completion chunks from the provider

eventStream emits events for each step. Depending on the response, a step can include:

• step.start and step.done (with optional usage on step.done)
• reasoning.start, reasoning.delta, and reasoning.done
• text.start, text.delta, and text.done
• tool-call.start, tool-call.delta, and tool-call.done
• tool-result.done

Event names use dot notation. Use eventStream for shared text, reasoning, and tool events. Use fullStream for the original provider chunks.

const { eventStream, fullStream } = streamText({
  apiKey: env.OPENAI_API_KEY!,
  baseURL: 'https://api.openai.com/v1/',
  messages: [{
    content: 'Tell me a short joke.',
    role: 'user',
  }],
  model: 'gpt-4o',
})

for await (const event of eventStream) {
  if (event.type === 'text.delta')
    console.log(event.delta)

  if (event.type === 'step.done')
    console.log('step usage:', event.usage)
}

for await (const chunk of fullStream) {
  console.log(chunk.object)
}

Image input

Make sure that the model accepts the image or audio input before you send it. xsAI does not detect this capability.

const { textStream } = streamText({
  apiKey: env.OPENAI_API_KEY!,
  baseURL: 'https://api.openai.com/v1/',
  messages: [{
    content: [
      { text: 'What\'s in this image?', type: 'text' },
      { 
        image_url: { 
          url: 'https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg', 
        }, 
        type: 'image_url', 
      }, 
    ],
    role: 'user',
  }],
  model: 'gpt-4o',
})

Audio input

Make sure that the model accepts the image or audio input before you send it. xsAI does not detect this capability.

const data = await fetch('https://cdn.openai.com/API/docs/audio/alloy.wav')
  .then(res => res.arrayBuffer())
  .then(buffer => Buffer.from(buffer).toString('base64'))

const { textStream } = streamText({
  apiKey: env.OPENAI_API_KEY!,
  baseURL: 'https://api.openai.com/v1/',
  messages: [{
    content: [
      { text: 'What is in this recording?', type: 'text' },
      { input_audio: { data, format: 'wav' }, type: 'input_audio' } 
    ],
    role: 'user',
  }],
  modalities: ['text', 'audio'], 
  model: 'gpt-4o-audio-preview', 
})

Result

The basic example collects text fragments in an array and prints that array.