>40,000ft. v. is classified.
Gulfstream V is famous jet used by celebs, also called the G5, and it is capable of reaching 51,000ft.
https://en.wikipedia.org/wiki/Gulfstream_V
Also, the following 2012 article titled "10 Outrageous Celebrity-Owned Private Jets" has interesting fact:
"Affectionately known as the "Google Jet" or "Google One," this is another symbol of Google's outrageous wealth. It has even acquired two years’ worth of landing rights at the prestigious Moffet Field, the notorious runway owned and operated by NASA. (Boeing 767-200)"
https://www.complex.com/sports/2012/08/10-outrageous-celebrity-owned-private-jets/