Starting in May, Ukraine's 3rd Army Corps began exploiting gaps in Russian lines just north of Sloviansk in eastern Ukraine's Donetsk Oblast. Five months later, the corps and its supporting drone units had cleared Russian troops from 277 sq km of northern Donetsk, inflicting what the corps says were 8,000 Russian casualties and pushing the Russian 20th and 25th Combined Arms Armies back across a key terrain feature: the Zherebets River.

On 14 October, the 3rd Army Corps declared victory in its Operation Vivaldi. "Four seasons of Vivaldi are over. But the music plays on," the corps wrote on Telegram.

It was unclear at the time what the corps meant. Its commander, Brig. Gen. Andrii Biletskyi, has since been seconded to lead Ukraine's new Center Group of Forces. But it's clearer now. According to at least two observers, Ukrainian troops have continued attacking along the Zherebets River—and have even crossed the river at several points.

If true and confirmed, the crossings could ratchet up the pressure on the battered Russian 20th and 25th Combined Arms Armies following their hasty and chaotic retreat from their former salient north of Sloviansk. The Zherebets should have been a natural defensive barrier for the Russians.

Sheltering on the river's eastern bank, the Russians could have rested, reset, and reinforced in preparation for a renewed offensive next year. But if the Ukrainians keep attacking, rest might be impossible. And that could force the Russians to rethink any plans for a fresh push toward Sloviansk and neighboring Kramatorsk, the last two big free cities in Donetsk.

But an extension of Operation Vivaldi isn't without risk for the 3rd Army Corps. If the corps pushes too far, too fast across a difficult obstacle, it could expose itself to counterattack.

Ukraine's "Vilvadi" counteroffensive in the Lyman direction has not stopped, despite claims to the contrary.

Ukrainian forces have made new advances in several different areas over the last couple of weeks, crossing the Zherebets River onto its eastern bank at multiple different…

— AMK Mapping (@AMK_Mapping_) October 26, 2026

Continuing counteroffensive

Ukraine's Vivaldi counteroffensive in the Lyman direction "has not stopped, despite claims to the contrary," the mapping account AMK Mapping explained on Monday after noting possible Ukrainian forces on the eastern side of the Zherebets in recent weeks. "Ukrainian forces have made new advances in several different areas over the last couple of weeks, crossing the Zherebets River onto its eastern bank at multiple different locations." AMK Mapping also noted that many Ukrainian assaults over the past month had been repelled and that casualties were likely rising.

AMK Mapping isn't alone. On Monday, mapper Suriyak also logged Ukrainian troops on the far side of the Zherebets in three key settlements: Makiivka, Novosadove, and Terny. "They are establishing a significant bridgehead," Suriyak wrote.

The possible Ukrainian river crossings could defy recent expectations. "The Ukrainians have continued their push and advancement toward the Zherebets River," mapper Clément Molin wrote on 20 October. "They have reached it at several points, and Russian forces no longer control any territory west of this river—with the exception of the forest east of Lyman."

Ukrainian-Russian war. Day 1700-1704:
Situation on Luhansk front: During the last two weeks, Ukrainian army has managed to secure new positions on the western bank of the Zherebets River, including the south of Makiivka and the rest of Novolyubivka. However, military… pic.twitter.com/zfi1Txv3eA

— @Suriyak (@Suriyakmaps) October 26, 2026

But Molin didn't expect the 3rd Army Corps to force the river, a risky maneuver under the best of circumstances. "Despite various rumors, I have not been able to confirm that the Ukrainians have actually crossed the river," Molin wrote.

Instead, he expected the Ukrainian corps to do what the defeated Russian field armies were trying to do: consolidate in new positions and get ready for the next round of major fighting, potentially next year. "For the time being, I believe the Ukrainians will focus on consolidating their gains and adopting a defensive posture."

If indeed the 3rd Army Corps has crossed the Zherebets, it's a possible indication that the corps still has some combat power in reserve—and is eager to prolong its momentum for as long as possible, even if that means heavier losses in risky river crossings.

A major clash could occur if and when the 3rd Army Corps tries to seize full control of Terny, which anchors the Russian line on the east bank of the Zherebets. Two years ago, Terny was the site of intensive fighting as Russian forces fought their way across the Zherebets on their long march toward Sloviansk. That battle was a costly victory for the Russians as they sent mechanized column after mechanized column across a drone kill zone toward Terny.

The worst outcome for the outnumbered Ukrainian troops in northern Donetsk may be a mirror image of the Russian march through Terny in 2024. Yes, the Russians eventually captured Terny and secured a bridgehead on the western bank of the Zherebets. But the Russians overextended as they kept pushing toward Sloviansk, roughly 40 km to the southwest of Terny.

It's that overextension that afforded the 3rd Army Corps the opportunity to counterattack and roll back the hard-won Russian gains. To preserve its own recent victory on the western side of the Zherebets, the 3rd Army Corps may want to choose caution. Ukrainian forces "need to organize a coherent and solid defensive line," Molin advised.

That may mean not attacking across the Zherebets—despite the temptation to do so.

The Ukrainian 3rd Army Corps' Operation Vivaldi—its secretive counteroffensive east of Sloviansk in northern Donetsk Oblast—started earlier than first reported, and by the time it ended on 14 October it had cost the Russians more than 8,000 troops, by the 3rd Army Corps' count.

It was a major Ukrainian victory in one of the most important sectors of Russia's 56-month wider war on Ukraine. But it could prove to be a temporary win, one the Russians may be able to partially reverse, if the administration of US President Donald Trump continues to throttle Starshield, the military version of Starlink that Ukraine's drones and commanders rely on.

The Ukrainians' former command and control advantage, largely attributable to once-reliable Starlink and Starshield access, was pivotal as Operation Vivaldi played out in the Donbas region in stages starting in March. That advantage shrank practically overnight on 14 October, when a new speed cap began cutting off Ukraine's Starshield terminals whenever they moved faster than about 160 km/h (100 mph).

The 3rd Army Corps attacked east of Sloviansk and north of Lyman as early as March, analyst and mapper Clément Molin concluded after scrutinizing official videos and interviews the Ukrainian defense ministry recently released. "The operation began much earlier than initially thought," Molin wrote.

We are now 5 months after the start of Ukraine's Vivaldi operation and it has now officially ended

A month after the operation was revealed, we know have much more information on the biggest Ukrainian success of the year.

THREAD1/18 pic.twitter.com/MgCoSv7Yhr

— Clément Molin (@clement_molin) October 20, 2026

The timing was probably no accident.

In early February, SpaceX, working from a Ukrainian defense ministry whitelist, switched off the thousands of stolen and smuggled Starlink terminals the Russians had been using.

That had the effect of grounding many Russian drones and blinding many Russian commanders. Taking advantage of the Russians' confusion, Ukrainian troops attacked in several key sectors: in Zaporizhzhia and Dnipropetrovsk Oblasts in the southeast, and east of Sloviansk in northern Donetsk.

The Donetsk attack expanded into a full-blown counteroffensive under conditions of strict secrecy as the 3rd Army Corps probed for weaknesses along the flanks of the Russian 20th and 25th Combined Arms Armies, then overextended along the axis between the Zherebets River in the east and the outskirts of the Sloviansk-Kramatorsk urban conglomeration in the west.

The Russians had been threatening to lay siege to Sloviansk and Kramatorsk, the last two big free cities in Donetsk Oblast, from two directions: the north and the south. Operation Vivaldi eliminated the northern threat—and at great cost to the Russian 20th and 25th CAAs.

Drones lead

Aerial drones and unmanned ground vehicles led the attack, taking the Russians by surprise. "For an offensive operation, the Ukrainians sustained relatively few casualties compared to previous engagements," Molin explained. "Conversely, the defending Russian forces suffered significantly higher losses, largely due to the rapid encirclement of at least three regiments, not all of which managed to escape the area."

It's unclear how many casualties the Russians suffered, but they might number in the thousands. The 20th and 25th CAAs were particularly fragile because the 3rd Army Corps and supporting drone units had been bombarding their supply line with so-called "middle strike" drones.

But many middle strike drones rely on civilian-style Starlink satellite terminals or the more rugged, better-performing Starshield. Now that the 3rd Army Corps has wrecked Russia's 144th Motor Rifle Division, which the Institute for the Study of War assessed on 20 October has effectively ceased to exist as an organized fighting force, and pushed the Russian survivors back to the far bank of the Zherebets River, the Ukrainians are probably "consolidating their gains and adopting a defensive posture," according to Molin.

But that defensive posture, protecting Sloviansk from a northern attack, depends on reliable communications and responsive drones. On 14 October, a new speed cap hit Ukraine's Starshield terminals, cutting the link on any drone flying faster than about 160 km/h. Who ordered it is disputed. Sources told Reuters the order came from inside the White House, and that Pentagon leaders were told the service needed to be slowed.

The Wall Street Journal reported that Musk himself ordered the slowdown, and that he and Trump discussed it soon after it became public. While Trump has denied ordering the speed limit, it's worth noting that the American president has become more overtly friendly toward Russia as his Republican Party looks likely to lose control of the US Congress in the November mid-term elections.

The speed limit renders many of the faster middle-strike drones unflyable. As a result, "Ukrainian drone strikes have diminished significantly following yesterday's crippling of Ukraine's Starlink/Starshield connections, Russian sources report," the military history account ChrisO_wiki wrote on X on 15 October, the day after the speed limit took Ukrainian operators by surprise.

A reduction in middle strikes on Russian supply lines could help Russian field armies recover from recent setbacks, including their retreat back across the Zherebets River. And if the communications confusion resulting from the partial loss of Starlink/Starshield connectivity persists, it could give the Russians the same kind of opportunity the Ukrainians had back in the spring.

An opportunity to go back on the attack—and an Azov communications engineer warned Euromaidan Press in February that the shoe might be on the other foot.

That's the worst-case scenario for the Ukrainians now that Operation Vivaldi has ended. The best case is that they get full Starlink and Starshield access back—or find command and control alternatives—and duplicate, in other sectors, the same success they enjoyed in northern Donetsk.

"Now that the northern flank of Donbas is secured, at least for some time, the focus will concentrate on the southern flank," Molin predicted.