Basil Jet wrote:

Apparently loads of enthusiasts knew in advance... us Usenauts seem to
be out of the loop!

https://www.youtube.com/watch?v=aSts1YN3MPc

I see that, as expected, the seats are described as harder than in the old
trains they're replacing, and they seem to be mainly longitudinal, as with
other TfL trains; the early pictures of the interior usually featured the
few transverse seats. At least the aircon works.