I understood (I think from one of these threads) that the current plan is merely to extend the Cardiff Bay - Pontypridd operation to Treherbert from or before the next timetable change in December, in which case it will be 2027 before they go public on other lines - but their planning director's presentation at a Transport Liaison Group session I attended on 10th July claimed that their introduction will set off a "Grand Cascade" of other stock which they expect to complete for the start of the May 2027 timetable.
Can you tell us more about this Transport Liaison Group? Is "Treherbert by December, the other lines next year" TfW's official stance on the 398 rollout now?
If so, it differs quite significantly from what TfW promised in the promotional video they released just 6 weeks ago, on 5 June:
We'll start running [the 398s] on services between Pontypridd and Cardiff Bay before rolling out to the Treherbert, Aberdare and Merthyr lines later this summer.
(Verbatim, but the bolding is mine.)
Is this no longer policy? Has TfW updated its public position on the rollout of the 398s since that video?
Incidentally, it was in response to that statement that a member of the forum wrote:
They need to stop promising dates... Late summer, but more like 2027-28.
This doesn't actually seem to be very different from what you were told by the planning director.