How to split unit stacks?

Ok, looks like when you click on your stack, a row of buttons appears above the information window offering the commands you can issue. For someone used to 1.0, they don't stand out very much.

It's the same in 1.0. There is no difference in interface. The split button is still there.

It's hidden under the hamburger menu on mobile, but only sometimes, other times it's on the main action strip while other things move under the menu. There doesn't seem to be any rhyme or reason to what's where AFAIK.