ExperimentalWarning: The fs.promises API is experimental

Yes, you can safely ignore this warning. If you want to suppress it (and all warnings), run your script with node --no-warnings instead of node.

In your example:

node --no-warnings `which autorest`

Updating to the latest node version (v12.6+) removes the warning.

I was at node@^10.15.1 which is an older version so I update it to 12.16.1 or 12.16.2 and it got fixed.