My guess a boy. Did it have any red showing a few weeks back? I have almost 9 week old BO's - one is obviously a boy with red comb and wattles, the other two have no red at all. Also, my boy of course does not have saddle feathers yet, but you can tell he's getting a bit of a jaunty roo tail.
One thing that people always miss - saddle feathers generally are not showing up until 13+ weeks (even later for some chickies). My two roos are just getting them in and they are 16 weeks old. My 9 week old BO cockerel has no saddle feathers but he's for sure a boy.
You might see a difference in the tail, or red patches, or a redder comb/wattle depending on the breed - but don't just go by saddle feathers unless it's a bit older of a chicken. "not crowing' doesn't work either - my last adult roo started to crow at 24 weeks and he was 100% roo much earlier.