📄 ai-sdk/docs/reference/stream-helpers/langchain-adapter

The @ai-sdk/langchain module provides helper functions to transform LangChain output streams into data streams and data stream responses. See the LangChain Adapter documentation for more information.

It supports:

LangChain StringOutputParser streams
LangChain AIMessageChunk streams
LangChain StreamEvents v2 streams

Import

import { toDataStreamResponse } from "@ai-sdk/langchain"

API Signature

Methods

toDataStream:

(stream: ReadableStream<LangChainAIMessageChunk> | ReadableStream<string>, AIStreamCallbacksAndOptions) => AIStream

Converts LangChain output streams to data stream.

toDataStreamResponse:

(stream: ReadableStream<LangChainAIMessageChunk> | ReadableStream<string>, options?: {init?: ResponseInit, data?: StreamData, callbacks?: AIStreamCallbacksAndOptions}) => Response

Converts LangChain output streams to data stream response.

mergeIntoDataStream:

(stream: ReadableStream<LangChainStreamEvent> | ReadableStream<LangChainAIMessageChunk> | ReadableStream<string>, options: { dataStream: DataStreamWriter; callbacks?: StreamCallbacks }) => void

Merges LangChain output streams into an existing data stream.

Examples

Convert LangChain Expression Language Stream

app/api/completion/route.ts

import { toUIMessageStream } from '@ai-sdk/langchain';import { ChatOpenAI } from '@langchain/openai';import { createUIMessageStreamResponse } from 'ai';
export async function POST(req: Request) {  const { prompt } = await req.json();
  const model = new ChatOpenAI({    model: 'gpt-3.5-turbo-0125',    temperature: 0,  });
  const stream = await model.stream(prompt);
  return createUIMessageStreamResponse({    stream: toUIMessageStream(stream),  });}

Convert StringOutputParser Stream

app/api/completion/route.ts

import { toUIMessageStream } from '@ai-sdk/langchain';import { StringOutputParser } from '@langchain/core/output_parsers';import { ChatOpenAI } from '@langchain/openai';import { createUIMessageStreamResponse } from 'ai';
export async function POST(req: Request) {  const { prompt } = await req.json();
  const model = new ChatOpenAI({    model: 'gpt-3.5-turbo-0125',    temperature: 0,  });
  const parser = new StringOutputParser();
  const stream = await model.pipe(parser).stream(prompt);
  return createUIMessageStreamResponse({    stream: toUIMessageStream(stream),  });}

On this page

Convert LangChain Expression Language Stream

Convert StringOutputParser Stream

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