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.