51-year-old software industry professional here near Chicago:
Jeans and shirt.
Will go for business casual for occasional internal meetings.
For customers, willing to match the customer, even if that means, gack, a suit and tie. (Although in 25+ years I can count those occasions on 1 hand and still have some fingers available for rude gestures.)
I detest dressing up for work and select jobs partially based on that. With my fashion sense, if I am judged by my wardrobe, I am already done.
I am finding this discussion fascinating. DH worked for Microsoft (left more than fifteen years ago) in management. No one wore suits but there was a serious sweater competition that went on (nice sweaters mattered more as you went up in management) as well as a pen competition. A really good pen mattered too. (DH had a silver fountain pen.) (These days they probably carry a tablet.) I have no idea if any of that still holds. Most of the programmers, even then, wore jeans and t-shirts, sometimes with holes in them. If they aspired to management, they wore nicer shirts and tucked them in.
DS is developing a product these days and regularly meets with investors. For those, he dresses up a bit: shirt with collar, nice pants, decent shoes instead of flipflops. Of course, he’s actually never owned a pair of jeans (he finds them uncomfortable). Mostly he wears shorts, t-shirt, flipflops. He does own a suit and wore it to a meeting in Boston with “financial people” a while back.
DH and DS are both software engineers at Apple. Jeans and a polo shirt for DH. Jeans, a t-shirt and a hoodie for DS