Apparently they withdrew from Izyum behind the Oskol river during the night. Unconfirmed reports are UAF crosses the Siversky Donets river largerly uncontested and are either fighting in or have already pushed the Russians out of Lyman.
All of this in the span of a few days without much resistance in crucial areas that took the allies months to take. No idea what to even say to this tbh.
It sounds like what happened was that Russia did not have enough forces to hold both Kherson and Kharkov regions, they chose to withdraw from Kharkov rather than lose troops and are now sending reinforcements there. The offensive drew a lot of Ukrainian troops from their fortifications into the open and while this is a big tactical success for Ukraine, it’s likely going to be a strategic failure in the long run. This is a pretty good overview of the situation in my opinion.