Until 2020, the US was part of the Open Skys treaty, which was specifically for allowing member states to fly unarmed spy aircraft in each others airspace. Chi

Until 2020, the US was part of the Open Skys treaty, which was specifically for allowing member states to fly unarmed spy aircraft in each others airspace. China was never a member, so wasn't covered under it, but Russia was until they withdrew in 2021. The only reason the US responded at all was internall politics. Geopolitically, we already assume that anything with line-of-sight to the sky is observable, and that this is probably good for geopolitical stability.