Max Verstappen and Lewis Hamilton, the two most successful drivers on the grid, were critical in testing of cars whose electrical hybrid systems promote unusual driving styles and make racing more strategic.
Four-time champion Verstappen branded the cars "no fun" and suggested they might be a factor in considering retirement, while seven-time champ Hamilton suggested the rules are too complex for fans to grasp.
It's a crucial season for F1, which expanded rapidly over the last decade by putting drivers' personalities centre stage and not focusing on technological detail.
"We need to stay calm because, as always when there is something happening as a new regulation, there's always the doubt that everything is wrong," F1 chief executive Stefano Domenicali said last week at testing.
Despite big changes, the top four teams are the same after Mercedes, Ferrari, McLaren and Red Bull all showed promise in testing.
Indeed, 2025's "big four" -- as McLaren boss Zak Brown calls them -- look set to be the "big four" in 2026 too.
They seem broadly similar on pace, with Mercedes and Ferrari perhaps having a slight edge in race simulations in testing.
At the final test, Ferrari revealed a rear wing that turns upside down for straight-line speed and an innovative mini-wing behind the exhaust. They also stood out as the fastest in practice starts after other teams, especially Mercedes, were sluggish off the line.
Rivals have praised Red Bull for mastering the electrical power technology, while champion Lando Norris and Oscar Piastri seem consistently strong again for McLaren, who use a Mercedes engine.
Mercedes' mix of power and reliability could make George Russell a true championship contender. There's extra attention on Mercedes' engine, which was fast in testing following weeks of speculation from rivals about its legality. Mercedes say the design is perfectly legal.
Some teams sacrificed the 2025 season to seek big gains in 2026, but it hasn't worked.
Even with star designer Adrian Newey in charge, Aston Martin were late to testing, unreliable, and often slower than new team Cadillac. Williams and Alpine have also struggled but Haas may be able to challenge the top teams.
The push by the FIA for a 50-50 split between power from the engine and from electrical hybrid technology means driving in 2026 is all about compromise.
Drivers in pre-season testing were revving the engines hard on the grid for a fast getaway, lifting off the gas on straights to charge the on-board battery and shifting down aggressively to first gear in corners. The FIA could intervene to tweak the regulations if the first few races throw up bizarre scenarios.
Standing starts off the grid required a tricky procedure in testing because the hybrid system doesn't kick in until 50 kph.
After some sluggish practice starts, tweaks have been made to the procedure, but that might not stop Ferrari, who identified the issue early and designed their engine to be quick off the line.
Hamilton delivered one of the most eye-catching moments of preseason by blasting past four cars in a practice start in Bahrain last week.
Fast starts might be extra important if overtaking is as hard as some drivers suspect.
Get ready to hear about 2026 cars being "energy-starved" on certain tracks, including Melbourne's Albert Park, which doesn't have as many heavy braking zones where the battery can charge.
If cars can't make full use of the hybrid system, the new "overtake mode" with extra power might be a waste of limited energy if it needs several laps to hit full charge and still leaves the overtaking car a sitting duck afterward.
Cadillac have joined as the 11th team with veteran race winners Sergio Perez and Valtteri Bottas, but face a year of learning after being consistently slow in pre-season.
Sauber is now Audi after a takeover by the German automaker, which is producing its own engines.
The Spanish Grand Prix leaves Barcelona after 35 years for Madrid's new Madring street circuit, while Italy's second race at Imola makes way and Barcelona stays on as the Barcelona-Catalunya Grand Prix.
