Workflow SDK now writes over WebSockets on Vercel

The Workflow SDK now sends event writes and stream writes to Vercel Workflows over a WebSocket by default, replacing one HTTP request per write, or per write group for streams. No code change is needed beyond upgrading to workflow@5.2.0 or later.

Once you deploy the upgrade, new runs use it. In-flight runs finish on the deployment they started on.

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npm install workflow@latest

Existing streaming code works as is. A step that writes a burst of chunks, like AI tokens, sends them over the WebSocket once it opens:

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import { getWritable } from "workflow";
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async function streamChunks(chunks: string[]) {
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  "use step";
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  const writer = getWritable<string>().getWriter();
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  for (const chunk of chunks) {
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    await writer.write(chunk);
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  }
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  writer.releaseLock();
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}
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export async function streamingWorkflow(chunks: string[]) {
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  "use workflow";
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  await streamChunks(chunks);
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}

Copy link to headingStreams keep pace with AI output

In a benchmark replaying an AI agent's token stream, v5.2.0, which writes streams over a WebSocket by default, delivered the full response 4.2× faster than v4.8.12, with no chunk delayed over a second.

Copy link to headingFewer HTTP requests for event writes

Every step start and completion is an event write, now sent over the WebSocket, so workflows with many steps make fewer HTTP requests. The added efficiency also improves performance and reduces costs. The queue handler opens the connection for every delivery.

Copy link to headingGet started

Read the Vercel World documentation to get started. If you're on 4.x, start with the upgrade guide, since v5 is a major release.