Twitter has apparently started a "9/80" work schedule where in a 2 week period you work 8 days at 9 hours a day, 1 day is 8 hours, and you get an extra day off.
I've worked a 4/10 and there were pros and cons, but the biggest issue I see is that there's still pressure against the clock even though we all know time with hands on keyboard or time working doesn't directly translate to productivity or value.
40 hours a week or 80 hours every 2 weeks isn't based on anything other than history and what workers rights were able to claw back. Henry Ford didn't reduce hours out of the goodness of his heart or care for people, he did it because of his bottom line. His attachment to Taylorism and scientific management, which focused on squeezing every ounce of productivity from their mindless, interchangable people resources (people are not resources, they are human beings, but Ford and Taylor didn't understand that, and many leaders still don't) says to make each step repeatable so they could slot in any worker to do it.
This is much different from the creative, complicated and complex, knowledge work in many fields, especially software development. The work we do today requires we have time to think, process, reflect, and collaborate together. To be creative, to try things, experiment, fail, and try again. We're not working an assembly line anymore, and the places that are - the best places that are, like a Toyota - learned that even assembly lines need to be run differently and empower their people to stop the line and fix problems (Andon cord)
Some places have been experimenting with overall shorter time working (32-36 hour weeks) and are seeing increased productivity, more effective meetings, less burn out, and happier employees who have more time to spend with or take care of themselves and their families.
There is no need for the 40 hour week in knowledge work anymore. Paint a clear and compelling vision, get people working together towards the goal, and trust your people. Reset your expectations to something reasonable - infinite growth is not reasonable, uncontrolled growth is not sustainable, and growth isn't a goal, vision, or mission in itself. If you want your organization to be here for the long term, execute strategy with long instead of short term thinking. Sometimes that means you go a little slower, but better to go slow and get where you want to go than to try to go too fast and wind up destroying everything.