Siemens Mobility is currently testing the first of the 94 new Piccadilly line trains that will be carrying passengers in London in 2025. These new trains have a lightweight design, internal improvements, and most significantly, air conditioning, which is a first for deep level trains. The challenge of fitting air conditioning into the small tube trains has been overcome by reducing the heat emitted from the engines and brakes and utilizing innovative train design. The new trains will have wider doors, improved information screens, and a capacity to carry about 10 percent more passengers than the current trains.
https://www.ianvisits.co.uk/articles/cool-commutes-ahead-inside-look-at-londons-new-piccadilly-line-trains-undergo-testing-in-germany-67513/