Red Bull is preparing to fire up its first 2026 engine in collaboration with new partner Ford.
"In the next few weeks, the first complete unit will be running on the test bench with the combustion engine, MGU-K and battery," Dr Helmut Marko told Speed Week at Spa Francorchamps.
"We are, we think, on a par with Mercedes in terms of development. I can't judge Renault, but Ferrari is behind us.
"With our incoming partner Ford, everything is also going according to plan."
That is despite the fact that, at the F1 Commission meeting held at the circuit on Friday, Red Bull's concerns about the greater influence of the electronic parts of the 2026 power unit were largely dismissed.
What the FIA has agreed to do is try to create a "significant reduction in the size and weight" of the 2026 cars including improved "energy management" to address Red Bull's concerns.
Marko said: "We're on track. But the fact that we are proposing a changed ratio in the hybrid drive envisaged by the FIA is also due to safety concerns.
"The batteries will then weigh 100 kilograms, the cars will be heavier and have to be bigger. We don't think that's a good thing," he added.
"We will be driving with e-fuels, so emissions will no longer play a role."
Red Bull has poached multiple engine specialists from Mercedes for its new engine subsidiary, but Marko denied that the team had to woo them with tripled salaries.
"No. Other factors played a role for these new employees - our spirit, our passion," said the 80-year-old. "We were attractive to them as racers.
"On a campus that now has 15 buildings, we have chassis and engine development in a single location - the only one to do this apart from Ferrari."
