Lewis Hamilton has questioned whether Formula 1's new rules are the "right direction" but said that the new engines are a "bold step".
Governing body the FIA has revealed plans for cars to be smaller, nimbler and more environmentally friendly from 2026.
Cars will be 30kg lighter, 10cm narrower and have engines with a near 50-50 split between electric and internal combustion power - and use fully sustainable fuels.
Hamilton, who has previously called for the cars to be made lighter, said: "It’s only 30kg so it’s going in the right direction but they’re still heavy.
"I have spoken to some drivers who have driven it on the simulator - I haven’t - and they said it’s pretty slow so we will see if it’s the right direction or not.
"But in terms of sustainability, particularly on the power-unit side, that’s a really bold step and it’s going in the right direction.
"We have just got to make sure the cars are efficient, fast and a step forwards and actually racing is improved."
The FIA described the concept at the heart of the 2026 rules as a "nimble car".
Active aerodynamics will be used to optimise the use of the new engines.
Cars will have front and rear wings that open on the straights to reduce drag and increase speed, but then close to increase downforce for cornering performance.
And overtaking will be facilitated by a power-boost system for a car following another.
This is instead of the current DRS (drag-reduction system) overtaking aid.
The new hybrid engines, which triple the amount of electrical power used, have attracted two new manufacturers into F1 in the shape of Audi and Ford, and persuaded Honda to reverse its decision to quit the sport.
Along with Mercedes, Ferrari and Renault, and the new Red Bull Powertrains company with which Ford is joining forces, there will be a total of six engine manufacturers in F1 in 2026.
FIA president Mohammed Ben Sulayem said: "The key features of the 2026 regulations are advanced, sustainable technology and safety.
"Our aim, together with F1, was to produce a car that was right for the future of the sport's elite category. We believe we have achieved that goal."
The rules are a part of F1's pledge to go net-zero carbon by 2030.
McLaren's Lando Norris said he was concerned that such a major change in rules would make the field less competitive again just as it was beginning to close up.
“There is going to be another change just as the sport gets exciting again," Norris said. "I guess there are reasons for it but I don’t want it to go the opposite way. Especially with how complicated it is.
"You could have massive gaps and then people are going to say it’s boring again. Right now it is as exciting as it has been for a very long time.”
The FIA's announcement on Thursday, on the eve of this weekend's Canadian Grand Prix, is the first confirmation of the 2026 chassis rules - the changes to the engines have been known for two years.
The new regulations governing cars include:
Minimum weight reduced by 30kg to 768kg
Width reduced by 10cm to 190cm
Front tyres narrower by 25mm and rears by 30mm, while retaining wheels of 18 inches in diameter
Active aerodynamics to reduce drag on the straights and optimise the operation of the new engines
A revised, partially flat floor to limit underbody aerodynamic 'ground effect' and reduce the need for the cars to be run very stiff and low - as they have been since the current rules were introduced in 2022.
Haas driver Nico Hulkenberg said the new cars will have "a lot less downforce, especilly in high-speed corners".
There has been criticism that the introduction of active aerodynamics as a fundamental operating characteristic of the car is unnecessarily complex.
But they have been employed because the drag of the cars needed to be reduced and braking distances increased so sufficient energy could be recovered during braking to supply the much greater electrical capacity of the power unit.
FIA single-seater technical director Jan Monchaux said: "The DRS on the rear wing will not be used to facilitate overtaking any more. It will be used by default on every straight by every car to drop drag levels, because this comes with some strong benefits for energy consumption.
"But also having higher top speed allows you to recover more [energy] when you're braking at the end of the straight."
On the new overtaking boost system, Monchaux said drivers would be allowed to use more electrical energy than their opponent if they were within a given distance of the car in front before the end of a lap.
The moveable aerodynamics have been required because the new engines are less efficient than the existing ones as a result of the removal for 2026 of the expensive and complex Motor Generator Unit-Heat (MGU-H) - a part of the hybrid system that recovers energy from the turbocharger.
Without the MGU-H, other means were needed to recover sufficient energy for the increased electrical power from the engine - which is being raised from 120kW to 350kW.
Head of aerodynamics Jason Somerville said the FIA had turned to moveable aerodynamics to reduce drag because otherwise the cars would have "experienced a severe drop in speed at the end of the typical main straights".
Other than the removal of the MGU-H, the engines will be similar to the existing ones - 1.6-litre V6 turbo hybrids.
A key change is the introduction of a 100% sustainable fuel.
When they burn, these fuels only put back into the atmosphere the carbon dioxide that was taken out of it to make them in the first place.
A study by Prof Felix Leach at Oxford University, funded by F1, found these fuels can achieve a reduction in life-cycle CO2 emissions of greater than 90% compared with fossil fuels.
These fuels can be used in almost any internal combustion engine.
The FIA is introducing an assurance scheme to "check the source of all the components used by fuel suppliers to produce the sustainable fuels" to ensure their credibility.
F1 chairman Stefano Domenicali said: "The new sustainably fuelled hybrid power unit presents a huge opportunity for the global automotive industry. The drop-in fuel has the potential to be used by cars around the world and dramatically cut emissions."
