Well the last time was Feb-March 2022 with 170,000 men and approx 2800 tanks.
The 100,000 is a Ukrainian military claim (Eastern military command) that could be very well a lie like their countless huge lies about the Russian forces and the war in general. (100,000 men, 900 tanks, 555 artillery pieces, 370 SP Guns).
They also claimed a Russian 2022-2023 winter offensive, even from Belarus- that never happened with 200,000-150,000 men for about 3 months. Both military and political top constantly lied about it, in retrospect these big lies was a scheme to manipulate public opinion and get more aid from the West.
If they spent the rest of the summer pumping up the ' 100,000 ' like in the winter 2022-2023 it could very well be public opinion 'damage' control for their currently failing counteroffensive. They also recently claimed that they lost 30% of their armored vehicles in the past 6 weeks which is an unusual thing for them to do (admit any sort of military incompetence).