HTTP Stream

Some places do not let SSE through: some edge runtimes, some mobile WebViews, or a proxy that strips text/event-stream. Stream newline-delimited JSON (NDJSON) instead. Each line is one JSON StreamChunk.

1. Return NDJSON from the server

Wrap the chat() stream with toHttpResponse():

import { chat, chatParamsFromRequest, toHttpResponse } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

export async function POST(request: Request) {
  const { messages, threadId, runId } = await chatParamsFromRequest(request);
  const stream = chat({
    adapter: openaiText("gpt-5.6"),
    messages,
    threadId,
    runId,
  });
  return toHttpResponse(stream);
}

To write the response yourself, write each chunk as JSON.stringify(chunk) + "\n" to the response body.

2. Connect from the client

Pass fetchHttpStream() to useChat:

import { useChat, fetchHttpStream } from "@tanstack/ai-react";

const { messages } = useChat({
  connection: fetchHttpStream("/api/chat"),
});

fetchHttpStream takes the same options as fetchServerSentEvents: url, headers, body, fetchClient, and dynamic functions. See Request Options.

On React Native, use xhrHttpStream with the same server. See React Native.

Resume a dropped stream

Pass a durability adapter to toHttpResponse. Then each line becomes an { id, chunk } envelope, and the client can continue a reply:

Reconnect. A dropped connection reconnects with Last-Event-ID. The adapter removes the replayed chunks that it already has.
joinRun(runId). It attaches to a run that already exists.

Add a GET handler for joinRun, with resumeHttpResponse:

import {
  chat,
  chatParamsFromRequest,
  memoryStream,
  resumeHttpResponse,
  toHttpResponse,
} from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

export async function POST(request: Request) {
  const { messages, threadId, runId } = await chatParamsFromRequest(request);
  const stream = chat({ adapter: openaiText("gpt-5.6"), messages, threadId, runId });
  return toHttpResponse(stream, {
    durability: { adapter: memoryStream(request) },
  });
}

// joinRun hits GET ?offset=-1&runId=... (replay only, no messages sent).
export async function GET(request: Request) {
  return resumeHttpResponse({ adapter: memoryStream(request) });
}