Red Bull sits at the top of Formula 1’s engine pecking order, according to a source familiar with the FIA’s determinations following the 2026 Monaco Grand Prix regarding the sport’s Additional Development and Upgrade Opportunities (ADUO).The ADUO upgrades are determined by the performance of the internal combustion engines (ICEs), and the FIA created a performance index to analyze each engine’s performance. Multiple factors — including engine torque, engine speed, MGU-K (motor-generator unit — kinetic) power and a weighting for how sensitively lap time responds to power output — will be evaluated across three review periods throughout the season.The first covered the first five races of the season: Australia, China, Japan, Miami and Canada. The FIA had 14 days to analyze the results and determine which ICE performed best. Anyone lagging at least 2 percent (or more) behind that engine manufacturer would receive an ADUO upgrade of some form.In plain terms, it means Red Bull’s rivals can keep developing their engines while Red Bull’s are frozen.Mercedes was widely considered the strongest engine as the team dominated the 2026 Formula 1 season, winning the first six races of the year and taking pole position at each. But The Athletic understands that the FIA’s ICE performance index showed that Red Bull’s unit is the best-performing.Mercedes was determined to be at least 2 percent behind Red Bull’s ICE, making it eligible for additional spending outside the cost cap — relief that can be used to fund one upgrade to its engine design this season and one next year.The rest of the engine manufacturers (Ferrari, Honda and Audi) were found to be over 4 percent behind, meaning they will receive two of those upgrades this year and two next season.It’ll take time for these upgrades to materialize, as it’s a multi-month ordeal and tests will need to be carried out. Lewis Hamilton told Sky Sports that it’s “an eight to 10-month project, so it’s not something we can just do next week.”The purpose of ADUO is to foster closer competition among engine manufacturers following the recent F1 technical regulation overhaul, in which teams needed to strike a near 50/50 split between electrical energy and ICE power.— Luke Smith contributed to this report.