For most of my adult life it was 9 hours. If I slept less, I eventually napped and caught up, or had an extra long sleep one or two nights.
About ten years ago it has been closer to 7.5 or 8 usually, but it depends on my thyroid. Sometimes it’s just 6 if I’m over medicated, or ten if I’m under medicated. Overall though, my need for sleep has declined. I guess that means I’m on my way towards dying.