Romain Grosjean has admitted that the real challenge for Haas will be keeping up with the lightning speed of Formula 1's in-season development.

The French driver and new American team have stunned F1 over the opening two race weekends in the life of Haas, scoring enough points to see Grosjean sandwiching the works Ferrari drivers for fifth in the standings.

However, the team's approach to F1 is also controversial, with the true independent Williams questioning if Haas is really a constructor.

"What Haas has done is good for him, but I don't know if that is really the way F1 should be going," technical boss Pat Symonds told the New York Times.

Haas team boss Gunther Steiner, however, defended Haas's close alliances with Ferrari and Dallara.

"We read every word of the regulations and got from Ferrari everything that was possible," he told Brazil's Globo.

"With this, our engineers designed the car and commissioned Dallara to build many parts including the monocoque.

"This is the only model to begin in F1 today if you are small like us. Those who have tried recently to do everything on their own arrived and were quickly gone."

While the basic Haas car is obviously good, Grosjean said that the next challenge will be to stay in front of established teams like Toro Rosso, McLaren and Renault.

"These people will improve and invest in development and we will have to do the same," said the Frenchman.

"The good thing for us is that our base is excellent. We do not have the structure of a large team and cannot compete with their speed and capacity for producing new parts, but we have a plan - although more modest - to develop our car."

The goal beyond that, boss Steiner revealed, is to conclude a commercial contract with the Bernie Ecclestone-led commercial rights holder.