langchain

@openuidev/langchain

Supported LangChain and LangGraph integration primitives for streaming OpenUI generative interfaces over AG-UI.

The package connects three pieces:

1. A LangGraph stream transformer converts protocol-v2 messages and tools events to AG-UI events on the remote custom:openui channel.
2. A server helper starts a stateless LangGraph run, adds strict AG-UI run lifecycle events, and relays that channel as Server-Sent Events.
3. OpenUI's agUIAdapter() consumes the response without LangChain-specific frontend code.

The APIs use Web-standard Request, Response, fetch, and ReadableStream. They do not depend on Next.js or DeepAgents.

Install

npm install @openuidev/langchain

The server helpers communicate with LangGraph over HTTP and do not load the LangGraph runtime. Install @langchain/langgraph only in applications that use the agent-side transformer:

npm install @openuidev/langchain @langchain/langgraph

@langchain/langgraph is an optional peer dependency. The supported range is declared in this package's peerDependencies so applications retain control of their LangGraph version.

The server helpers require an agent-protocol-v2 server that supports both the custom:* and root lifecycle event channels. The tested local-server baseline is @langchain/langgraph-cli 1.4.x; older servers that reject the lifecycle channel are not supported.

Add the agent transformer

The transformer works with any agent that accepts LangGraph streamTransformers. Here is the minimal DeepAgents setup:

import { openUIStreamTransformer } from "@openuidev/langchain/transformer";
import { createDeepAgent } from "deepagents";

export const graph = createDeepAgent({
  model: "openai:gpt-5.5",
  tools: [getWeather, getStockPrice, searchWeb],
  systemPrompt: SYSTEM_PROMPT,
  streamTransformers: [openUIStreamTransformer],
});

openUIStreamTransformer() converts assistant text, tool-call deltas, tool results, and run errors into AG-UI events. LangGraph forwards those events remotely under the custom:openui channel.

Add a server route

createLangChainStreamResponse accepts any Web-standard Request, so it can be returned directly from Next.js and other compatible route handlers:

import { createLangChainStreamResponse } from "@openuidev/langchain";

export const runtime = "nodejs";

export async function POST(request: Request) {
  return createLangChainStreamResponse(request, {
    apiUrl: process.env.LANGGRAPH_API_URL ?? "http://localhost:2024",
    assistantId: process.env.LANGGRAPH_ASSISTANT_ID ?? "agent",
    apiKey: process.env.LANGSMITH_API_KEY,
    debug: process.env.NODE_ENV !== "production",
  });
}

Use prepareInput when the graph needs additional fields from the browser request, such as a provider-managed conversation id or model selection:

return createLangChainStreamResponse(request, {
  apiUrl: process.env.LANGGRAPH_API_URL ?? "http://localhost:2024",
  assistantId: "agent",
  prepareInput: ({ messages, requestBody }) => ({
    messages: messages.slice(-1),
    conversationId: requestBody.threadId,
    model: requestBody.model,
  }),
});

The route expects a non-empty { messages: Message[] } body in AG-UI format and returns a JSON 400 response for malformed input. It converts text and multimodal user content to LangChain messages. Complete assistant tool-call and tool-result pairs are preserved; only incomplete calls and orphaned results are removed before starting the stateless run.

Each call uses a temporary LangGraph thread and makes a bounded cleanup attempt before closing a normally completed response. Pass cleanupThread: false when the thread must remain available for local debugging. On serverless platforms, pass the platform's waitUntil-style registration function through the waitUntil option so cleanup can survive a client disconnect. Upstream response bodies and registered graph ids are redacted from stream errors by default; pass debug: true only in a trusted development environment to include them.

Connect OpenUI

The route returns AG-UI SSE with RUN_STARTED and RUN_FINISHED/RUN_ERROR lifecycle events, so the browser only needs OpenUI's AG-UI adapter:

import { AgentInterface, agUIAdapter, fetchLLM } from "@openuidev/react-ui";

const llm = fetchLLM({
  url: "/api/chat",
  streamAdapter: agUIAdapter(),
});

export function Chat() {
  return <AgentInterface llm={llm} />;
}

Lower-level streaming

Use streamOpenUI when a route needs to build the LangGraph input itself:

import { streamOpenUI } from "@openuidev/langchain";

const body = streamOpenUI({
  apiUrl: "http://localhost:2024",
  assistantId: "agent",
  input: { messages: [{ type: "human", content: "Hello" }] },
  signal: request.signal,
});

return new Response(body, {
  headers: { "Content-Type": "text/event-stream" },
});

Cancelling the returned stream or aborting the supplied signal aborts both upstream LangGraph requests.

API

• openUIStreamTransformer() from @openuidev/langchain/transformer — LangGraph stream-transformer factory that publishes message and tool events on custom:openui.
• createLangChainStreamResponse(request, options) — complete AG-UI request to LangGraph response path for stateless chat routes.
• streamOpenUI(options) — lower-level protocol-v2 runner and custom-channel relay.
• CreateLangChainStreamResponseOptions, PrepareLangChainRunInputContext, StreamOpenUIOptions, and LangChainInputMessage — exported TypeScript types.

See the repository's examples/langchain-chat for a complete local and LangGraph Platform example.