Average 10. When I'm really tired 12 to 14. I can do with as little as 8, but if I go south of 8 for more than 2 days in a row I will not be productive. The day is kind of foggy.

OTOH I have noticed that in these foggy days, especially in the afternoon, I get very creative insights. I just write them down because I can't use them on that day, but after a good night of sleep these insights come very handy in the next days.

EDIT: that's before I stopped coffee. My sleep pattern has been irregular these last few days. I don't enough data yet, but I seem to need less sleep. I guess my average will go below 10, maybe down to 9h. I'll see in a year.

EDIT2: I'm obviously not counting "crash coding" sessions. I may stay awake for 36h, with serious pain in old injuries past the 24h mark, and hallucinations past that 36h limit. My productivity seems low after 24h, so I don't bother and just go to bed.