I went to Nepal two years ago. The standard insurance of my Mastercard Gold specifically excluded medical assistance/transportation for acute altitude sickness from the coverage (and rescue operators are reluctant to intervene without proof of proper insurance coverage).

As a precaution (having read about it on forums) I had taken an additional insurance from a French shop specialized in hiking and mountaineering (le Vieux Campeur) to cover more events.

Good thing I did because I ended up having to be evacuated for something that was initially considered as acute altitude sickness and turned out to be a lot more life threatening once in the hospital.