Where do they say their network stack is userspace?
I watched the video but the last 10 minutes and I missed it.
To clarify, the whole networking stack isn't userspace. They still have the classical BSD networking stack. I think the userspace networking stack is used automatically by system libraries like URLSessions and this new Network.framework library. They introduced their userspace networking stack during last year's WWDC: https://developer.apple.com/videos/play/wwdc2017/707