On 1 May 1929, seven Ukrvozduhput K-4s flew in formation from Kharkov to Rostov, Sochi, Mineralnye Vody and Tbilisi.
Early production examples were used on trial services between Kharkov and Moscow, Mineralnye Vody, and Baku.
The existence of the aircraft had only recently been announced by Pravda which declared it was " victory of the utmost political importance" since it had been built with steel produced in the USSR rather than imported.