Ferrari's 2015 engine has matched the level of performance of the dominant Mercedes power unit, according to Niki Lauda.
The Maranello squad has made a clear step forward in performance this season, and the introduction of an upgraded power unit at the Italian Grand Prix erased Mercedes' power advantage, says Lauda.
"This year to do better than Ferrari we had to make a lot of progress," Lauda told Italy's Autosprint magazine.
"Since they introduced the updated engine at Monza, I would say that they matched us in terms of power and efficiency.
"The 20bhp advantage we had is now gone. Now we are at the same level of power: we know for certain because of the reference we have."
Lauda, a non-executive chairman at Mercedes, believes 2016 will bring the German squad's dominance to an end, as he reckons there is very limited progress it can make.
"The picture will change in 2016, because in F1 you can't sustain your technical superiority for a long time," Lauda added.
"We know the others can catch up. When you are at the limit of the performance of the regulations it's difficult to make big progress, which is easier for those behind us."