Early production examples were used on trial services between Kharkov and Moscow, Mineralnye Vody, and Baku.
On 1 May 1929, seven Ukrvozduhput K-4s flew in formation from Kharkov to Rostov, Sochi, Mineralnye Vody and Tbilisi.
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.