Verstappen and Daniel Ricciardo have used the Spec C in the last two races, while the Renault Sport factory team itself and fellow customer McLaren have stayed with the Spec B due to reliability concerns.
Ricciardo described the Spec C as ‘encouraging' while Verstappen finished second last time out in Singapore despite their weekends being affected by engine mapping issues.
However, Red Bull will downgrade this weekend in Sochi with an eye to the Mexican and Brazilian Grands Prix towards the end of the season.
“Our C-spec cannot run at high altitude in Mexico and Brazil,” said Verstappen.
“We also knew since we took the C-spec on that we had to take another B at one point.
“I think this (Russia) is the best place to do it. Also to have a few more spare parts in case something breaks.”
The switch will lead to both the Dutchman and Australian taking as yet undetermined grid penalties.
However, it clears the way for them to be competitive in Mexico City, a venue which team principal Christian Horner believes is realistically the team's “only shot” at another win this year.
Verstappen also noted that the Spec C is not necessarily a superior race engine, but does deliver in qualifying.
“The C-spec has a bit more power in qualifying, but it's the same or maybe a little slower in the race,” he explained.
“But it's all about qualifying. We would always want to take another tenth or 1.5 tenths if the engine gives it to you. That's why we decided to take the C-spec.”
Practice for the Russian Grand Prix starts tonight at 1800 AEST.