Envelope mass versus bolometric-luminosity diagram comparing the pre- and post-outburst positions of HOPS 383 (green data) with previously reported Class 0/I low-mass protostars detected in X-rays (blue and red data). The border zone between Class 0 (M_env >  M_⋆/ϵ, where ϵ = 0.5 is the local star-formation efficiency) and Class I (M_env <  M_⋆/ϵ) protostars is defined by M_env = 0.1 L_bol (constant accretion; dotted line) and (exponentially decaying accretion; dashed line). The protostellar evolutionary tracks are shown from 0.01 M_⋆, f to 0.9 M_⋆, f, where M_⋆, f is the final stellar mass. The rising time along the tracks is indicated by white dots every 10 000 yr.