Taiwan recently admitted that it had an F-16 training squadron in the United States. This is normally kept quiet by Taiwan and the United States as part of an unofficial American agreement to not sell Taiwan new jet fighters in return for China not trying to take Taiwan by force. The recent revelation was caused by a training accident that left a Taiwanese F-16 dead and there was no way to hide that.
The Taiwanese F-16 squadron has been in Arizona since 1997 and that was known to the Chinese. This training arrangement came a few years after Taiwan bought 150 F-16s and the uproar from the Chinese led to an “arrangement.” The way this arrangement works, if no one publicizes the presence of Taiwanese F-16s in Arizona China pretends that there is nothing to complain about. China has also not made a big deal out of American firms helping Taiwan upgrade its F-16s. Apparently China will also not complain if the United States sells Taiwan several dozen U.S. Marine Corps AV-8 Harrier vertical takeoff ground support aircraft. These AV-8s will be refurbished before Taiwan gets them. China will probably complain about the AV-8, eventually if only because they would probably be used to attack any Chinese amphibious force trying to land in Taiwan. Meanwhile China does have over 1,200 short range ballistic missiles (with non-nuclear warheads) aimed at Taiwan.