Why Carlos Sainz sealed Williams and Mercedes sealed

This, according to Bernie Collins, the former head of race strategy at Aston Martin.

Williams recently confirmed their multi-year agreement with Sainz, marking a significant shift in the Spaniard's career trajectory.

Sainz's decision came after Ferrari announced earlier this year that he would be replaced by Lewis Hamilton, the seven-time world champion, in 2025.

This news left Sainz contemplating his future, but he ultimately chose to align himself with Williams, who are set to benefit from new technical regulations coming into play in 2026.

Williams' long-standing relationship with Mercedes, renowned for producing one of the most potent power units in F1, was a decisive factor for Sainz. Collins noted that this partnership played a crucial role in Sainz's choice. "When you look at the current grid for next year, it's unlikely there will be significant changes from this season," Collins remarked on the Sky F1 podcast.

"Between Williams, Alpine, and Audi, Williams is probably the strongest team out of those three for the upcoming year."

Looking further ahead to the 2026 regulations, which promises to place greater emphasis on engine performance, Collins highlighted that Williams' established link with Mercedes could offer Sainz a more promising future.

"The upcoming regulations will shift more focus onto the engine," she explained. "Williams' commitment to Mercedes, a brand with a history of strong engines in new regulation cycles—like in 2014—is an advantage.

"Even if Williams doesn't secure podiums or wins next year, 2026 might present better opportunities. It's a more forward-looking choice."

In contrast, Alpine, another team interested in Sainz, are set to abandon their current engine project and switch to Mercedes power units, though no formal agreement has been announced. Audi, making their debut in F1, remain an unknown quantity, which may have added to Sainz's decision to choose a more stable environment.

Collins has underscored that the uncertainty surrounding Alpine's engine deal and Audi's entry made Williams a more attractive option. "We don't yet know which engine provider Alpine will choose, and Audi's entrance remains uncharted territory. Williams, with their secure Mercedes partnership, represents a less risky choice as we approach the new regulations."

With the F1 season currently on its summer break until 23 August, Sainz's switch to Williams in 2025 promises to be a significant storyline as the sport gears up for its next chapter.