Both Ferrari and Mercedes look set for additional engine upgrades this season and next after Red Bull's engine was judged to be the best by the FIA.
In a document seen by ESPN, the internal combustion engine of Red Bull's newly-built power unit has been ranked ahead of Mercedes in what is called the ICE Performance Index.
Mercedes -- the engine which has won every race this year -- was judged second, with Ferrari, Audi and Honda ranked in the next category and due additional upgrades.
The FIA has not yet officially communicated the ADUO upgrade allocations, but teams were made aware ahead of the Monaco Grand Prix.
Ferrari's Lewis Hamilton appeared to confirm so after finishing second at Sunday's Monaco Grand Prix.
"I think the news came out either yesterday or today that Red Bull have the most powerful engine, Mercedes second, and then we're behind," Hamilton told Sky Sports. "So, we've now got these tokens to try and develop and close the gap."
Under F1's new rules, the sport's V6 hybrid turbos are split almost 50-50 between the ICE and the controversial electrical systems, which has led to an unprecedented focus on battery harvesting and deployment.
But the ICE portion of that 50-50 split has been the subject of what's called Additional Development and Upgrade Opportunities (ADUO) and has seen the FIA measure the engine performance of each manufacturer across the first six races of the season.
ADUO was created as a mechanism to prevent the competitive field from being too spread out in terms of outright performance.
Hamilton downplayed the notion that ADUO will lead to a sudden change in the competitive order.
"That's like an eight-to-10-month project, so it's not something we can just do next week," he said. "We'll be pushing as hard as we can to see how we can close it out."
The news that it is Red Bull -- not Mercedes -- who are deemed top might be seen as a surprise, given Mercedes has won all six races so far this season.
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Many in the paddock expected Mercedes' engine would be the class-leading ICE under the ADUO mechanism.
Red Bull's engine project -- officially titled Red Bull Powertrains -- started earlier this decade under the leadership of Christian Horner, in conjunction with Ford, focused solely on the 2026 season and the new engine regulations.
Red Bull's F1 team has not been a factor at the front of the pack this year but Max Verstappen claimed a podium in Canada and then qualified on the front row in Monaco, only to stall on the grid.
The ADUO system takes engine speeds, torque and other metrics into consideration to form a performance metric. It's a highly complicated process, which includes a weighting to account for power sensitivity on lap time across measured laps.
The FIA has been measuring the performances of each ICE all year but has been reluctant to specify exactly how, wary that manufacturers might try to game the system if they knew what exactly was being looked at and how.
Manufacturers trailing by between 2 - 4% will be given one opportunity to develop its power unit this season, and one more in 2027, as well as an extra £3 million outside the cost cap. Those trailing by 4% or more will get at least two opportunities in 2026 and two further opportunities in 2027, as well as an extra £6.25 million at least going forwards.
The FIA has not confirmed the scale each manufacturer has been judged on -- there are different allocations for teams between 2 - 4%, 4 - 6%, and 8% or more.
Honda's underperforming engine was expected to be due a major ADUO boost given its horrible start to the season with Aston Martin.