Ukraine has had ATACMS and been using them against Russia for some time.

This was a previous red line for Putin.

Putin has called all the land in Ukraine occupied by Russia to be Russian.

But in Oct 2023 Ukraine took out two airfields in Berdyansk and Luhansk They used cluster munitions to tear up a bunch of helicopters.

https://youtu.be/43SWOS0lSf4?si=2joim2CIRXOylglk

So to your point about escalation ATACMS have been in use for two years. Against land Putin considers to be part of Russia. The difference is Berdyansk and Luhansk are actually Ukrainian.

The recent change is to use these weapons within Russia.

Ukraine has had ATACMS and been using them against Russia for some time.

This was a previous red line for Putin.

Putin has called all the land in Ukraine occupied by Russia to be Russian.

But in Oct 2023 Ukraine took out two airfields in Berdyansk and Luhansk They used cluster munitions to tear up a bunch of helicopters.

https://youtu.be/43SWOS0lSf4?si=2joim2CIRXOylglk

So ATACMS have been in use for two years. The difference is Berdyansk and Luhansk are Ukrainian.

The recent change is to use them within Russia.