Formula 1's new rules era formally began on track in Barcelona on Monday with seven of the grid's 11 teams hitting the track on the opening day of 2026's closed shakedown week in Spain.

Behind closed doors at the Circuit de Barcelona-Catalunya with no media present, the teams who chose to run on day one were Mercedes, Red Bull, Racing Bulls, Haas, Audi, Alpine and the all-new Cadillac team.

Teams are allowed to run on three days of the five-day test in which the focus is reliability running over performance given the all-new nature of 2026's cars and engines.

McLaren and Ferrari had already confirmed they would not be running on Monday, while Williams are not attending the test at all due to delays with their 2026 car.

Aston Martin, meanwhile, confirmed on Monday that they intended to run on Thursday and Friday - the test's final two days - only as the world waits for the first look at Adrian Newey's debut design for the team.

Although there are no live timings during the test, with 'official' pre-season testing running not under way until the first of two tests in Bahrain from February 11, it is understood that Isack Hadjar set Monday's pace in the new Red Bull RB22 - which is running the team's own power unit for the first time.

The Frenchman had set the morning pace and, although he was usurped by Mercedes' George Russell midway through the afternoon, he ended up going faster with a day-best 1:18.159.

Russell was second, 0.5s back, with Franco Colapinto third in the newly-Mercedes-powered Alpine. The Alpine had brought out one of three red flags in the morning due to a sensor issue on the A526 before returning to the track.

Kimi Antonelli completed the morning's running for Mercedes and was fourth fastest.

"It's a massive learning," said Antonelli about the nature of F1's new-look cars.

"We've been trying to tune the power unit and the car, and obviously this afternoon the car has improved a lot, and it's a constant learning.

"The most important is trying to get the running, as many laps as possible, in order to tune the power unit and car in the best way possible."

On Mercedes' 2026 power unit, which many have tipped to prove the early class of the field, Antonelli added: "The team did a really good job and driveability, which was a big question mark, seems to be good so far.

"Obviously, it's early days, and that's why with the running we will discover a lot more about the car and the PU and we'll be able to see where it's lacking or where it's actually good, but, so far, the package is feeling good."

The opening day marked a milestone for the Cadillac team - the grid's new 11th entrant - who were on track alongside the existing F1 outfits for the first time.

Valtteri Bottas marked his return to the sport after a year's absence by driving the car for the first time in the morning before team-mate Sergio Perez - who gave the challenger its debut during a Silverstone shakedown earlier this month - took over after lunch as the Mexican gears up for his own F1 comeback.

More to follow...

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