https://www.youtube.com/watch?v=OmtSI3N57kM
https://en.wikipedia.org/wiki/City_Rail_Link
"Although the trains are capable of having extra cars added in groups of three, the CRL station platforms, as originally specified, would not be long enough to accommodate nine-car trains. The proposed new capacity is 54,000 passengers per hour with the station platforms to be made longer so they can take the longer trains..." https://en.wikipedia.org/wiki/City_Rail_Link#Capacity_forecast_forces_platform_enlargements
9 car trains are possible for Auckland, because there isn't anything like a VMV to thwart it.
https://www.cityraillink.co.nz/meet-your-stations
https://en.wikipedia.org/wiki/Waitemat%C4%81_railway_station#Capacity
https://en.wikipedia.org/wiki/Waitemat%C4%81_railway_station#Electrification
