I went from Xi’an to Lhasa and in Xining I had to change to the Tibet Train.
The train cars are equipped with oxygen outlets, further more the cars are standard Chinese train sleeping cars.
I took a hard sleeper which was fine for me.
Next morning when I woke up we were going through these fascinating landscape and had an unbelievable clear blue sky. The train went then up over 5000 metres above sea level to go then down to Lhasa (3762) again.