It has previously been reported that Mercedes had pushed back first deliveries of the AMG One hypercar due to complications with its F1-derived powertrain, but this is the first time the company confirms it.

Mercedes-AMG’s head of product management, Michael Knoller, spoke with Road & Track about the upcoming hypercar, revealing that the company has already informed customers of the delay and that first deliveries of the AMG One will begin in 2021.

“When you make F1 technology street legal you have to go through a journey with the customers,” he said. “We had some challenges, but now we’ve reached a tipping point.”

Related: Porsche Considers Using Aborted F1 Engine For New Hypercar

Mercedes-AMG Project ONE-1

These challenges apparently included getting the hypercar idling at a steady 1,200rpm in order to meet emissions-test requirements.

“You have leakage in the throttles in Formula One and nobody cares, because it runs at a 5,000rpm idle,” said AMG boss Tobias Moers last year. “At a 1,200rpm idle, you have to meet the emissions regulations. You need a stable, proper idle. If it’s unstable, your emissions are unstable.” Knoller now also admitted that meeting noise regulations was also pretty challenging.

Mercedes-AMG Project ONE-3

The upcoming Mercedes-AMG One will share its powertrain with the 2017 F1 car, meaning a hybrid 1.6-liter V6 engine. The powertrain will use the same electrically spooled turbocharger, MGU-K electric motor and liquid-cooled batteries with Lewis Hamilton’s single-seater, but will also add an extra pair of MGU-K motors at the front axle for full torque vectoring AWD.

Other revisions include the powertrain’s redline being limited to 11,000 rpm, down from the F1’s 14,000 rpm, with the total output expected to exceed the 1,000 HP barrier. Mercedes promises a 0-200 km/h (0-124 mph) sprint in less than six seconds and a top speed in excess of 350 km/h (217 mph).