Edit: I know many people working 4-day work weeks are self-employed, but I'm curious for those who are looking for employment.
After half a year in a company you have a right to get into part time work, but there are some requirements that have to be met and every employer I talked to in my career so far was very... unhappy when asked about it.
I asked that isn't four days easier to allocate than five days as it means less allocation? Would it be easier if I would work 6-days week? Never got answer.
Most of the excuses are bullshit. The truth in consulting business is that they don't get as much money from you (even if you cut 1/5 from your salary).
Well, that's true of most jobs. If your job is directly tied to revenue production, you're certainly counted on to bring in more money than your (fully-burdened) cost. But I can see it being a particular problem in consulting.
I would be sure to ask in advance. Since there's a huge shortage of developers right now (at least in the midwest where I am) you might have a good argument to make if a company is in need and willing to negotiate.
Always, always, always ask. You never know when an employer is willing to negotiate to get a good developer on their team.
Here in WA State, over 40 hours in 1 week is mandatory 1.5x overtime pay. So 9-hour days would give you 5 hours of overtime pay one week, and short you 4 hours the other week. Many workers would be OK with that, and I guess government contractors probably just pass on the overtime to the taxpayers.
Which is probably why you rarely see that work schedule (alternating 4x9 & 5x9) outside of government.