At least currently it seems likely this was done with FPV drones flown by SBU-led sabotage groups operating inside Russia, not by "traditional" long-range drones flying all the way from Ukraine. This would also explain why the defensive measures failed so immensely. 4/4

These are major and expensive losses for Russia that can't be replaced quickly.

Additionally, the air base in Belaya, roughly 4300 km from Ukraine, has been hit. Also Dyagilevo and Ivanovo air bases are burning. This is a very, very successful day for Ukraine. 3/

Ukraine has struck multiple strategic bombers in Olenya, Murmansk oblast, 1800 km from Ukraine. This is one of the most successful drone strikes against against Russian air bases in the entire war. The extent of the damage is yet unclear, but I can already say it's significant. 1/