HQ attacks can now only be launched once an enemy faction has full knowledge of your HQ. Knowledge is currently added when a traitor mission is failed, or when a support is called against a target near HQ. Knowledge diminishes slowly over time as long as it hasn’t reached 1. Moving HQ will reset knowledge, as long as their wasn’t a previous HQ nearby recently.
The attacks themselves are still mostly specops air, but benefit from improvements to combat behaviour. Support artillery and UAVs are also used to assist. These attacks can also use limited ground troops.