My coworkers, particularly middle managers in the US expressed some envy, but applauded my negotiation and support me. I let my partner in engineering know before I said yes because I didn’t want them being surprised.

Self-moderation:

I have to be incredibly intentional about limiting my working hours. No one’s going to tell me to go home and I’ll feel the pressure to stay so I just have to commit.
No checking email or work slack after working hours. No. Matter. What. Nothing on my personal devices. In fact my work laptop never leaves my office or my back porch. Not allowed in personal spaces. Like I get this is a “everyone should do it thing” but when I was working five days it just happened. Now I’m intentional about it never happening.
Having four days has honed my ability to both prioritize and say no. But it also means those stupid meetings that are easier to say yes to and just kind of be there, I’m much more actively turning down. It’s hard to have defend the boundaries. But it’s worth it.