What is F1’s ‘ADUO’ engine upgrade system?

F1 has unveiled the 'ADUO' (Additional Development and Upgrade Opportunities) mechanism, set to be introduced for power unit manufacturers from the 2026 season. Designed to promote competitive parity, the FIA will monitor Internal Combustion Engine (ICE) performance across three seasonal periods, creating a performance index based on factors like torque, engine speed, and MGU-K power. Under this system, manufacturers lagging 2% or more behind the leader will be granted specific development allowances. A deficit of 2-4% allows for one upgrade in the current and following seasons, while deficits of 4% or greater permit two upgrades per period. These adjustments are not a 'Balance of Performance' measure but a cost-cap relief initiative, allowing manufacturers extra expenditure allowances ranging from $3 million to $11 million to close the technical gap.