The 2 newbuilds (currently under construction at China Merchants Jinling Shipyard in Weihai) are a larger/lengthened version of the "Stena E-Flexer" design used in the ships Stena Edda, Stena Embla, and Stena Estrid.
Mr. Olsson also stated Stena was contemplating an investment case for a battery pack to be fitted to the ships. This would allow the ferries to run on battery power part of the time while they are at sea in order to reduce exhaust gas emissions. The design incorporates a shore power connection meaning that the vessels can switch off their engines while alongside at a suitable port.
The as-yet-unnamed vessels (Estelle and Ebba) are both scheduled for deliveries in 2022. Their arrival will displace the smaller Stena Baltica and Stena Scandica (fka Stena Mersey and Stena Lagan) from the Nynashamn-Ventspils route, should plans remain unchanged. It is likely Baltica and Scandica will then be transferred to another route of Stena Line.