Agile optical amplifiers must preserve constant gain and flatness over a wide range of input conditions to meet the needs of reconfigurable optical networks. Though routers and switches used to perform system protection or network reconfiguration feature slow transition times, reported theoretical and experimental analyses of the dynamics of agile EDFAs have focused on fast, sub-microsecond input-signal transitions. As a result, only low population inversion, one- or two-stage baseline amplifiers practically provide acceptable transient performance over the entire dynamic and wavelength range of operation. On the other hand, advanced, versatile optical amplifiers, which are highly desirable to perform system-level controls such as gain adjustment or reconfigurable wavelength add-drops at mid-stage, feature large excursions in these input conditions. In this paper, we discuss the line-transient times in view of today's switching technologies and Standards and provide experimental evidence of the suitable performance of advanced agile amplifiers at system switch speeds. The amplifier used is a very high-performance, agile device, which relies on a 3 μs feedback loop. Input transients up to 15 dB were studied, showing excursions smaller than 1 dB and steady-state gain errors no larger than 0.2 dB.