Do you have ANY evidence that they are using Pakistani airspace? If so, remember to post the links here.
Afghanistan is a landlocked state, the only countries that control a border with it are Pakistan, China, Iran and the central Asian states. So unless the US has figured out teleportation where it instantly arrived with aircraft over Kabul, it used the airspace for one of those countries. We can rule out Iran(for obvious reasons, Iran has shot down US drones before and is the relationship is generally hostile), we can rule out China, b/c the chinese aren't going to allow armed flights over their territory for operations. so that leaves the central Asian states and Pakistan. Out of the Central Asian states, they are also fairly landlocked, with the only way to reach them is via flying over Russia, or flying over Azerbaijan(The Azerbaijani forign office has been quarreling with the state dept over the karabakh issue, to its very unlikely that they are simultaneously cooperating on US operations into central asia using their airspace, not to mention that it will likely upset the Russians, which isn't in Azeri interests, as there is little gain for them) .. The Russians are in the middle of fighting a war with the US, via Ukraine serving as a proxy, so its very unlikely they will allow overflights of armed US aircraft for operations, they are also unlikely to let CSTO states to allow these flights(much of the CSTO states have their air defense systems integrated into the Russian Air Defense system), this likely rules out Kazakhstan, which has little to gain from upsetting Moscow over the sensitive topic(US operations and presence in Central Asia, in the soft Russian Underbelly) for Moscow. Now this leaves Turkmenistan, which is also unlikely b/c Turkmenistan has made it a point to be a neutral state since its existence, akin to a central asian Switzerland, Turkmenistan is also one of the few states that has tried to keep a good relationship with the Taliban, and one of the few states that have accepted the Taliban Ambassador to Dushanbe(its not recognition, as no state has recognized the new afghan govt, but in terms of diplomacy its the next closest thing), Turkmenistan has very little reason to allow an overflight for US operations into Afghanistan. This then leaves Pakistan via a process of elimination, as the only viable option. In addition to being the closest route into Afghanistan(the central asian route is far too long, and there are no close airbases in that region, so any flight would have to fly from continental europe and fly over several countries, and deal with more difficult logistics). The Pakistan Route makes the most sense, t it has a long history of usage, so much so that it has been nicknamed "the boulevard", where US planes would take off from Al Udeid Air Base, and fly over Balochistan and then into Kabul. Another element to note is right after the airstrike, Bajwa spoke to US officials and comes out with a statement, calling for IMF aid to Pakistan, and generically emphasizing Pakistan's "cooperation" with the US. All these elements when analyzed would point to the likely entry point for over the horizon operations into Afghanistan being Pakistan. One should also note the removal of Imran Khan, who was critical of the US, as a element that would be conducive to a rapprochement with the US especially on matters relating to Afghanistan.
map of region for the geographically challenged:
https://i.pinimg.com/originals/b8/0b/fe/b80bfe25f29c8746dfc5f73be438d392.gif
