I'm super new at this so don't have an opinion....but man that's gotta be hard to sex with such a dark underside!!! I have a couple of b.albiceps slings coming soon..definitely something about them I do not look forward to haha everything else about them seems awesome!
That's a tough one and I would wait for a moult. Did I say female on another photo you posted, because now I'm not sure? Females will have a distinct 'moustache' of contrasting white hairs, but I am not sure at one point that becomes very obvious. My girl has them, but she is probably closer to 4.5".
@VanessaS it’s so contradictory because the dark hairs and almost impossible to catch them like this. Where would the white hairs be located if you don’t mind me asking? Mine could be closer to 4, but I need to pull her/him out and measure maybe tomorrow.