Bi- and multi-specific antibodies offer new ways to engage complex disease biology, but greater functionality also introduces important therapeutic design challenges. This session will share practical lessons from the development of next-generation antibody formats, exploring how teams balance target selection, molecular architecture, potency, selectivity and safety. Discussion will highlight approaches to controlling immune activation, improving tissue-specific activity, reducing off-target effects and preserving an effective therapeutic window. Drawing on real development experience, participants will examine how early design decisions influence preclinical performance, translational potential and clinical strategy, helping developers create purposeful complexity rather than complexity for its own sake.