According to Ukrainian officials, the remaining Russian units are surviving largely on limited air resupply, a tactic that cannot sustain long-term operations inside the city.
"Supply by air bridge alone is not something that allows them to hold out for long," Trehubov said.
While Russian forces continue to launch multiple assaults along the Kupyansk axis each day, Ukrainian officials say those attacks lack the manpower and reserves needed to change the balance on the ground.
"At this stage, they simply do not have additional capabilities to somehow restore the situation," Trehubov said.
The Kyiv Post also reported that Russian military bloggers and war correspondents have begun openly conceding that Kupyansk is no longer under Russian control, marking a notable shift in Kremlin-aligned messaging.
"An entire wave of messages appeared saying that Kupyansk is gone," Trehubov said. "Even Russian propagandists have switched to a line acknowledging that the city is no longer under their control."
Ukrainian officials stressed that Russia never fully reestablished control over Kupyansk after its liberation in September 2022, aside from a brief occupation during the early phase of the invasion.
"In reality, it was never fully taken by them in order to be ‘lost,’ aside from a short period in 2022," Trehubov said.
Efforts by Russian units to dig in within the city’s northern districts have failed, leaving those forces unable to withdraw or receive reinforcements, Ukrainian officials said.
"They themselves now admit that the defense of the city by the same units that entered and tried to secure positions in the northern districts has failed," Trehubov said.
Combat continues outside the city, particularly from positions across the Oskil River, though Ukrainian forces maintain control of Kupyansk itself.
Ukraine’s General Staff said Russian troops carried out five attacks in the Kupyansk sector Dec. 24, all of which were repelled near Petropavlivka, Pishchane, Zahryzove and Kupyansk.
Trehubov said a recent Ukrainian counteroffensive further disrupted Russian efforts to stabilize the front.
"The counteroffensive came as a surprise for the enemy," he said. "Right now, they simply lack the resources to regain control."
Kupyansk, a key rail and road hub in the Kharkiv region with a prewar population of about 27,000, has long been a focal point of Russian territorial claims.
The city was briefly occupied during the opening months of Russia’s full-scale invasion in 2022 before being liberated by Ukrainian forces later that year, a history Ukrainian officials say Moscow has repeatedly tried to obscure through disinformation.