Fab-arm exchange is a technique that produces bispecific antibodies by taking advantage of the spontaneous half-antibody exchange of IgG4 antibodies. IgG4 mostly works by blocking or modifying targets and has a modest effector function. To efficiently generate bispecific antibodies, Fab-arm exchange technique merely needs to mix two IgG4 antibodies with distinct target specificities and incubate them under mild reducing conditions for a predetermined amount of time. Due to its great efficiency, versatility, controllability, and versatility, this technique has been applied extensively to a wide range of targets and disease areas.