The lineage of the OK class stretches back to 1981, when Intercontinental A (ICA) was introduced at the European Championship as a secondary direct-drive category alongside Formula K. ICA ran for 26 seasons before being superseded in 2007. One of its notable champions was Stefano Modena, who completed back-to-back ICA European titles in 1984. The ICA World Cup was introduced in 2006 — the final year of ICA regulations — and was won by French driver Mike Courquin.
In January 2007, the CIK-FIA replaced ICA with the KF2 class, adopting 125 cc Touch-and-Go (TaG) water-cooled two-stroke engines producing 34–36 hp. KF2 karts used hand-operated front brakes, CIK-approved chassis, an electric starter, and a centrifugal clutch limited to 15,000 rpm. Minimum weight was set at 160 kg including driver for national events, and 158 kg for international events. In 2010, KF2 became the primary direct-drive category at the World Championship, replacing KF1. When KF1 was discontinued at the end of 2012, KF2 was renamed simply KF and again became the top-tier World Championship class.
In 2016, Original Kart regulations replaced KF following the latter's perceived failure within the karting community. Reduced entries at international events and overly restrictive technical rules drove the reform. The new OK regulations stripped away much of the electronics present under KF and mandated push-starts rather than electric starters.
The current OK technical specification centres on eight key features: a 125 cc direct-coupled, water-cooled two-stroke engine with mixed lubrication; a valve inlet in the piston skirt; a screw carburettor with a maximum diameter of 24 mm; a maximum engine speed of 16,000 rpm; a power valve at the exhaust; a single rear brake with hydraulic control; premium tyres with a medium gum compound; and a minimum weight of 150 kg including driver. Engines, chassis, bodywork, brakes, and tyres are subject to CIK-FIA homologation. Tyres and fuel for each category are selected annually via a call for tenders.
OK — counting its ICA and KF predecessors — has been contested at the European Championship since 1981, and at the World Championship or World Cup level since 2006.
Lorenzo Travisanutto of Italy is the only driver to have won multiple OK World Championships under the current regulations. Other notable World Champions include Nyck de Vries, who went on to become Formula E World Champion in 2020–21. Lando Norris, who became Formula One champion in 2025, is counted among the class's prominent alumni.
At European Championship level, Stefano Modena and Andrea Kimi Antonelli are the only drivers to have won multiple OK European titles. Antonelli repeated Modena's back-to-back feat in 2021. Other notable European Champions include Formula One World Drivers' Champions Michael Schumacher and Max Verstappen.
The OK class and its predecessors form the traditional entry point into professional motorsport for drivers who aspire to Formula One. Generations of champions — including Ayrton Senna, Michael Schumacher, Fernando Alonso, Kimi Räikkönen, Lewis Hamilton, Sebastian Vettel, Nico Rosberg, Max Verstappen, and Lando Norris — passed through international karting before reaching the pinnacle of the sport.
The OK-Junior class uses the same engine and transmission as OK but is restricted to drivers aged 12 to 14, with modified specifications for mufflers, air boxes, carburettors, and speed limiters. The KZ and KZ2 categories pair a 125 cc engine with a six-speed gearbox, while Superkart uses a 250 cc gearbox engine. Under FIA President Mohammed Ben Sulayem, the FIA introduced the OK-N and OKN-Junior categories to reduce the financial barriers to competitive karting.