What technique do I use for these sleeves?

I love the taper at the wrist on this sweater and would like to implement it in a project I’m working on. Does anyone have any idea as how to do this?

Interesting pattern. It may be that increases similar to one of these (maybe the lavender swatch)

are used on a cuff up sleeve.
If it’s knit shoulder down, it might be a k2tog on successive rows. It could even be a kind of traveling cable.
You’d have to try out some of these techniques to see which gives you the look that you want.