Rival Formula 1 teams will be keeping a very close eye on Alpha Tauri next year.
Red Bull's second team began the year with a highly uncompetitive car amid rumours of sale - and ended the season with a much closer relationship with Red Bull Racing.
"At 18 of the 22 grands prix, Alpha Tauri showed up with new parts, eight times to such an extent that one could almost have spoken of a B, C or D version," said Auto Motor und Sport correspondent Michael Schmidt.
But it's not just the rate of progress that competitors are finding alarming, as Red Bull's junior team even ended the season with the rear suspension of the title-winning RB19.
"No one can do the slow corners better than them now," says McLaren boss Andrea Stella.
Then known as Toro Rosso, the Faenza based team could have reignited similar synergies with its parent team several years ago, "but the engineers had their pride and believed they were as good as (Adrian) Newey", said Red Bull's Dr Helmut Marko.
That is now changing, with Alpha Tauri engineers to even have their own building at Red Bull's Milton Keynes campus.
And that is what the competitors are most worried about - that Alpha Tauri's progress actually helps the already-dominant Red Bull Racing team.
The FIA's Nikolas Tombazis, however, says the governing body has a close eye on working relationships between teams. "We visit each team every two to three weeks," he confirmed.
Christian Horner's increasing power is also a concern to rivals, as he is believed to have championed Daniel Ricciardo's return to F1, Laurent Mekies' installation as Alpha Tauri boss, and a new major sponsor for the junior team - Visa.
"If Alpha Tauri competes for fifth place next year, there will certainly be calls for us to sell the team," one unnamed Red Bull official said.
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