KF1 is the top level of karting. It is open to the best drivers aged 15 and up.

This class used to be called Formula A and has changed since January 2007 when CIK-FIA decided to replace the 100 cc water-cooled two-stroke engines with 125 cc Touch-and-Go (TaG) water-cooled two-stroke engines (KF type). Chassis and engines must be approved by the CIK-FIA. Minimum weight is 160 kg with driver.

Karts are equipped with an electric starter and clutch. The engine rpm is limited at 16,000 rpm. Top speed is around 85 mph (140 km/h), depending on circuits.

As the Formula One of karting, KF1 has very high costs and drivers typically spend $100,000 per year to compete. It is needed to finance a lot of practice, training and testing, team costs, chassis and engines, tires and parts, and a quite a lot of traveling. Most teams in this category are factory teams or financed by chassis or engine manufacturers.

Drivers typically compete in national competitions, then move into international racing in the KF3 or KF2 classes where they have to finish in the top 34 to qualify to compete in KF1. Once in KF1, drivers either stay for a few years to improve their skills before moving on to car racing, or they become professional kart racers and race in KF1 until they retire. Many successful racing drivers and all current F1 drivers except for Vitaly Petrov started their careers in karts.