Both Toro Rosso drivers will receive grid penalties at this weekend's Russian Grand Prix as engine supplier Honda introduces a new power unit upgrade.
The Japanese manufacturer is hopeful that the latest specification will offer "more performance in the long term" and comes one race ahead of its home grand prix at Suzuka. However, the changes in power unit components mean both Pierre Gasly and Brendon Hartley will start towards the back of the grid with penalties this weekend in Russia.
Next year, Honda will supply Red Bull with engines and the Sochi update is believed to form the basis of the 2019 power unit. The focus is expected to be on the internal combustion engine, but the FIA will confirm exactly which components have been changed when the power unit first runs on track later this weekend.
Asked how big a step the upgrade would bring in performance, Gasly said: "We need to wait and see exactly all the positives from it, but we will have something, some insight. We will surely start from the back of the grid, it's been a while since we had an update so it's all positive."
Red Bull's drivers Max Verstappen and Daniel Ricciardo are also expected to receive penalties this weekend in order to add another B-spec Renault engine to their pool for the rest of the year. Renault has said the C-spec engine the Red Bulls have used at recent races is not ready to run at high altitude in Mexico, meaning Ricciardo and Verstappen needed to make an engine change at some point before that race regardless.