The Boeing SST and the Concorde both (if the SSt would have been introduced into service) fly a parabolic flight path with the top of climb (TOC) or apogee being Flight Level (FL) 600 or 60,000 feet above mean sea level (MSL).
Here in the U.S. under our aircraft certification rules, both would have required the pilots to be wearing pressurized breathing apparatus or masks anytime they were above FL450 (45,000 feet). We have to wear the quick donning pressurized masks anytime that one crewmember leaves the c0ckpit when in flight above 35,000 feet, as well. However the Concorde was certificated under British/European rules and no such requirement exists.
The Concorde is designed with a relatively small cabin area and very small windows. (Originally it was designed with no windows, rather with television monitors until the PR folks said that wouldn't do). The massive engines (4) provide enough bleed air to pressurize the aircraft even if two windows were to blow out.
By the way, although "fighter" aircraft can reach FL600, most of their activity is in the mid-30,000 foot range.