Odd, I worked at Goldman Sachs in London in approx. 1999-2001 and visited the New York office a few times and remember it being the usual "smart/casual" (veering to very casual). When did it smarten up?
I don't recall New York being much more casual, but it might have.
Back then, in NY, they put a foosball table on the 26th floor (IIRC) of 85 Broad St for the quants ("Strats"), in an effort to compete as an employer with the first dot.com boom (foosball = cool, right).
Once the tech bubble burst, the foosball table was gone pretty quickly though! :)
The London head office was in a listed art deco building on Fleet Street, beautifully renovated with a great gym and waterfall, quickly dubbed the "NASDAQ 5000 memorial waterfall"... (It only hit 5000 again in 2015)
Did put on a tie when making presentations to the desk, though.