Not that many different stocks now. The 4 sub-surface lines were given S7 or S8 stock according to platform length, and while it's entirely possible an S7 does sound different from an S8 I wouldn't count on it because these are basically the same train.

So that's a change from 5 stocks (two A variants, two C variants and a D) across four lines to two (S7 and S8) in terms of the rolling stock. The deep tube lines will all get variations on the 2024 stock, likely in 2027 although I believe the announced date still clings to "late 2026" but for now are all distinct.

The NYC subway (and elevated) trains were also originally operated by several different private companies, and there are still at least two major types of rolling stock (used separately on "A" division and "B" division lines). Maybe less variation than London, but I really couldn't say having never been to London.

Chicago's "El" and subway system AFAIK, uses the same rolling stock on all lines though there may be a couple of different generations of cars in service.