TfL have put out a press release discussing a change in the way the London Overground Electrostars will be financed - they've essentially sold them to a bank and are leasing them back, which improves their cashflow and gives them the option of walking away in 2027 and buying new ones. Anyway, hidden at the bottom is this note:
In its final configuration, it is intended the fleet will comprise 54 4-carriage trainsThe original order was for 44 trains, a mix of 3 and 4 car trains and a total of 152 carriages. They then ordered three more whole trains plus extra cars to make the fleet all 4-car, taking the total to 188. The latest news adds an apparent 7 more trains and brings the total to 216.
A brief mention of a follow-on order did appear in the recent board papers, but this the first indication of its size.