Defense Minister Sergei Shoigu said (video, Sputnik report) that 300,000 reservist will be mobilized. Conscripts and people currently studying will not be send to Ukraine.
He also said that, so far, 5,937 Russian soldiers have died during the war in Ukraine. (This number does not include the militia of the DPR and LPR, or the Wagner group, who have done most of the frontline work and thus have had higher losses.) Shoigu puts Ukrainian losses at some 62,000 killed and some 50,000 wounded. (I regard this as a low estimate.) Russia's total military reserve, people who have previously gone through military training, is 25 million. It also has the equipment to arm those forces.
There are rumors that the Ukraine is preparing for an all out offensive, mobilizing and preparing new units from Kiev and further west for one big push against the Russian and allied forces. It will take a few months to prepare for this. The Ukraine will need much more equipment and ammunition from the 'west', including 'western' tanks and infantry fighting vehicles, and has yet to train troops to be able to use it. It is likely intending to start the offensive only in spring.
The call up Russia announced now may have the intent to draw Kiev into a premature launch of its general offensive. The mobilized Russian troops will take about three months to be ready for war. Russia could thus launch its own offensive during the winter season. In the meantime constant defensive work will continue to severely degrade the Ukrainian units which are currently on or near the frontlines.
With a force of an additional 300,000 troops, far beyond the 100,000 to 150,000 engaged now in the war, the Russia forces could change their tactics from the slow grind that is happening now into a larger scale maneuver war with heavy strikes into the operational depth of the Ukrainian army.
Belarus, allied with the Russian Federation, is also in the process of getting ready for war. It could, as it had threatened before, cut of the supply lines from the 'west' into the Ukraine in the western part of that country.
Should current Ukrainian attacks on civilians and infrastructure in Russia and the Donbas regions continue, we can expect that the Russian forces will start to degrade Ukrainian infrastructure on a large scale. The electricity and railway networks would be the primary targets.
Update:
Some two weeks ago a successful Ukrainian offensive led to the retreat of Russian troops in the Kharkov region. That at least is the 'western' version of that story. A different narrative is that the Russian troops intentionally withdrew from the region to raise Russian calls for an escalation of the war. The Izium withdrawal was thus probably a mere catalyst for 'starting in earnest':
The Russian public, which at first did not fully understand why the war was necessary, has since grown in its awareness. It now understands the big game that is played against its country. It may soon demand to adjust the level of resources put into the war to the one needed for a decisive victory. Polls will clarify if or when that point is reached.
That is why Dima concludes that: "We can say that today was the best ever [..] day for the Russians in the territory of Ukraine."
It is now probably assured that they will be liberated. One way or another.
I also believe that the withdrawal from the Izium region, which left behind a significant number of pro-Russian civilians under deadly threats from fascist 'filtration' groups, will be the catalyst for a significant escalation on the Russian side.
Finally the gloves are coming off.
They did last night. I was up way too late in a Russian chat.
That’s the problem with the great news...it happens when I am usually about to go to sleep.