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We investigate the optical response of nanolasers of diffraction-limited volumes operating at 300 K and 1,55 μm, in terms of coherence and dynamics. In such lasers with ill-defined threshold, we propose and demonstrate that it is possible to distinguish between spontaneous and stimulated operation can be made on the grounds of the dynamical laser response. We also demonstrate that light produced from such lasers is not fully coherent even four times above threshold, due to the small number of photons and emitters.