As far as I know, the default strategy was both cars on mediums, same as every other car on grid.
Lando was called into box on the same lap as Osc 'box to overtake', but they cancelled it as Oscar went it. Then towards the end of next lap, when Lando was supposed to box, Will asked him 'do you want hards? we'll take them to the end, I need answer quickly' and Lando said yes.
Considering hards were two steps harded than mediums, I think they were pretty hard (no pun intended

) to keep in the right spot in cold conditions and were therefore considered inferior strategy by every team.