I know I can duplicate a tab with the keystroke cmd+d, but I only know that because I was told that on these forums. It's not discoverable because right-clicking a tab doesn't expose the fact that tabs can be duplicated, or show the keystroke. If right-clicking included duplicate as an option, and showed the keystroke I think lots more people would find this great feature, and, I think things would be easier for those who prefer to point and click rather than use key strokes.
Try to right-click on a host in the list of hosts;-)
@bart.busschots Thank you for this suggestion. This easy-looking feature is not possible at this moment – Core Shell uses native tab control exactly same as Safari and Finder, the problem is Apple makes menu customization a private API, only apps made by Apple can use the API, that's insane. I hope Apple could open this API one day.
@mikael.fransson Bart was talking about tab duplication, not host duplication 
Yeah, I saw that but to me it's basically a 1:1 relationship. I rarely open more than one ssh session to a host and going back to the tab with the list of hosts to double click on one will now do the duplicate tab with not much extra effort. Duplicating hosts and editing the properties is how I create new hosts 99% of the time. Just thought I'd point out that the duplicate host right-click existed.
Thanks for the explanation — hopefully Apple open up those APIs at some stage 
We clearly have very different uses for CoreShell — I rarely if ever want or need to duplicate hosts, but I want to duplicate tabs all the time to tail a log file while I run a command etc..