The contract notice has been published for the replacement fleet -
"Description of the procurement Following the Cabinet Secretary for Transport’s announcement on 3 September 2024 that a replacement is to be sought for the High Speed Train (HST) fleet which operates intercity routes between Glasgow, Edinburgh, Aberdeen and Inverness, ScotRail (SRT) is seeking expressions of interest, and from those who prequalify, tenders for:
1. the supply of a single fleet/class of existing rolling stock to operate its intercity services; and
2. the provision of technical support and spares supply arrangement to enable SRT to maintain the fleet.
The InterCity Replacement Fleet (The Fleet) must demonstrate improved reliability and availability, reduced emissions and operating costs compared to the current HSTs. The Fleet must be capable of operating on existing Network Rail infrastructure on SRT’s intercity corridors with min. changes to achieve a statement of compatibility and safety validation.
The Fleet shall be of sufficient size to operate min. 19 daily passenger diagrams plus sufficient spare trains for maintenance. The average passenger diagram operates approx 220,000 miles p/a. The supplier of the trains will be required to refurbish The Fleet (as needed) before it enters passenger service to provide SRT customers with a reliable and comfortable journey, attractive environment and suitable facilities.
The Fleet will be required to operate in reliable passenger service until at least 2035 and may be required (in whole or in part) until 2040 without further refurbishments. The full Fleet and maintenance support services should enable 19 passenger diagrams to operate from Dec 2027 (backstop date), and SRT reserves the right to exclude fleets which are not expected to be introduced by this date. SRT prefers The Fleet is in reliable passenger service sooner, with the aim from Dec 2026."
Basically looking for a fleet of trains in existence as opposed to something new due to the leadtime involved - maximum in service 3 years from now and also talking about being in service only for approximately a decade.