Airbus
Depends on if AutoThrust is disconnected by the instinctive disconnet buttons on the thrust levers whereby they thrust will match Thrust lever position (TLA). If disconnected by pressing the Autothrust Pb then depending on what mod state will get "Thrust Lock" or matching TLA
Boeing
Max thrust for each phase of flight computed (either manually or by FMS) and displayed. Autothrust will maintain melected speed by using upto the max for that mode.
Simplistic (like me) but hope it helps