[dreen]

Websockets still not generally available, ticket opened in 2009 https://issuetracker.google.com/issues/35886348

[dudus]

There's really no reason to use AppEngine these days. I believe it still exists for legacy apps. You should be using Cloud run. Cloud run support WebSockets[1].

If you already have an AppEngine App you can always keep it and create a CloudRun app to handle the WebSocket part and they communicate well.

[1]: https://cloud.google.com/run/docs/triggering/websockets