Asked for it in the initial interview. I thought I was going to give back a day in negotiation and do 4d/w, but it didn't come up. I figured I could always come back after and ask for more hours if I need the money or couldn't fill the time.

I have heard of exactly two other devs at 3d/w in the last 5 years so I wouldn't pin any hopes on that, but there's plenty of people at 4d/w.