General Electric GE90 Takeoff: 0.278 lb/lbf/h (28.3 kg/kN/h) Cruise: 0.545 lb/lbf/h (55.6 kg/kN/h) Source: https://en.wikipedia.org/wiki/General_Electric_GE90#Specifications
I assume this is typical for a modern HBPR turbofan.
Of course, as altitude rises, the reduced air density means the fan has less airflow, causing less thrust to be created. But then again, the bypass ratio does not change, so the core airflow also decreases by the same amount as fan airflow. So fuel flow should be decreasing too! So why is the TSFC TWICE as bad for cruise as takeoff? Is it because of losses in the fan duct increasing rapidly with speed?
(By the way, I know the higher speed helps reduce the seat-mile consumption, but still.)
EDIT: Wait what the? RB211, another HBPR turbofan, has almost no difference between cruise and "sea level" https://en.wikipedia.org/wiki/Thrust-specific_fuel_consumption