Force India is not expecting to receive the upgraded Mercedes engine before the end of the 2015 season, according to driver Sergio Perez.
Mercedes spent its remaining seven engine development tokens ahead of the Italian Grand Prix and introduced the new spec at the Monza race. Though the factory team has had the new power unit for three races it is yet to give the upgrade to any of its three customers, Force India, Williams and Lotus.
Mercedes has lingering concerns over reliability of its new spec, heightened by Nico Rosberg's troubles with the upgraded power unit when it was introduced in Monza, and Perez says this is a factor in the decision.
"At the moment all we are hearing is [Mercedes] are checking the reliability to see if it is working well," Perez said. "From there we will see. We are not planning to get any of the full spec for the rest of the year, is what I heard from the team. Hopefully for next year we get it."
The Mercedes token spend was not primarily focused on improving performance and was done "tactically" to aid the development of its 2016 engine. One of the primary goals was to make further improvements on reliability for next season.
Perez says the gains in performance from the upgraded power unit would not be too substantial for Force India.
"What we heard from Mercedes is that is not a big step forward, so the team is not too concerned about not getting the engine."
Asked if not getting the power unit should be expected as a customer team, Perez replied: "Exactly, yes."
The Mexican driver also confirmed he will be moving on to a fourth new power unit at this weekend's Russian Grand Prix, the final change he can make before incurring grid penalties.