World Champions are using 2015-spec V6 hybrid right from the start of testing in Jerez.
Mercedes has hit back at rumours it might begin the 2015 season with 'old' engines for strategic reasons.
It has been suggested the title-defending team, expected to still be wielding a significant advantage this year, might race in Melbourne with the 2014-spec unit and therefore keep all 32 development 'tokens' up its sleeve for the championship fight.
But as the W06 was officially unveiled at Jerez on Sunday as the opening winter test began, the German team's engine boss Andy Cowell insisted: "I can assure you that we have the 2015 engine in the car right from the first test.
"We have incorporated many new ideas in all areas, from internal combustion to energy conversion," he is quoted by Auto Motor und Sport. "After the 12 days of testing we will decide what we can bring with reliability to the start of the season in Melbourne.
"Our goal is to be using the best possible engine as early as possible," Cowell said.