Vercel Workflow SDK Moves Writes to WebSockets.

Vercel Workflow SDK now sends event and stream writes over WebSockets by default. The change replaces the separate HTTP request previously used for each event write, or each group of stream writes.

According to the Vercel changelog, existing workflow code does not need to change. Builders only need to upgrade to workflow@5.2.0 or later and deploy the new version.

For workflows that emit frequent updates, this means fewer HTTP requests. An AI agent streaming tokens is the clearest example. Once the WebSocket opens, a step can send a burst of chunks over that connection rather than creating repeated HTTP requests.

Vercel benchmarked the update by replaying an AI agent's token stream. Version 5.2.0 delivered the stream 4.2 times faster than version 4.8.12. No individual chunk was delayed for more than one second in the newer version.

Stream delivery

4.2× faster

workflow 5.2.0 compared with 4.8.12

Longest chunk delay

Under 1 second

no chunk exceeded one second

Required version

5.2.0 or later

WebSockets are used by default

The same transport change applies to event writes. Reducing the number of HTTP requests improves performance and lowers the request costs associated with those writes.

Code using getWritable() continues to work as before. A workflow can get a writer, write each chunk and release the lock without adding WebSocket connection logic. The SDK handles the transport underneath it.

The upgrade boundary follows deployments. New workflow runs started after the updated deployment use WebSockets. Runs already in progress remain on the deployment where they began and finish there.

To install the current release, update the package with npm install workflow@latest, then deploy normally. There is no migration step for existing event or streaming code.

This deployment behaviour avoids switching the transport underneath a running workflow. It also means test runs started before and after deployment can use different SDK versions until the earlier runs finish.

What are Vercel Workflow SDK WebSocket writes? They send Workflow SDK event writes and stream writes to Vercel Workflows over a WebSocket by default. This replaces one HTTP request per event write, or per write group for streams.

How do I enable WebSocket writes in Vercel Workflows? Upgrade to workflow@5.2.0 or later and deploy the update. Existing streaming code can remain unchanged, and new runs will use the WebSocket transport.

Which Vercel plan includes Workflow SDK WebSocket writes? The changelog does not specify plan availability or pricing.