An expression is proposed for a threshold discriminating between classical quasi-steady-state amplification and a strong pumping regime where a new dynamic behavior shows up in plasma-based extreme-ultraviolet (XUV) lasers. The criterion derived is applied to laser systems currently investigated in various laboratories. It is found that only high-gain XUV laser systems can be driven in that dynamic regime, associated with Rabi oscillations. For those systems, the small-signal dynamic gain accounting for the exponential amplification of the laser intensity is shown to be significantly smaller than the adiabatic value usually inferred from numerical simulations.