In new product development for proteins, monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs), it is common for the phase 1 and final commercial product presentation to be undetermined. Liquid, frozen liquid and freeze-dried solid formats may all be under consideration pending stability outcomes. Despite this uncertainty, clinical trials should be performed with a formulation representative of the final product. An appropriate freeze-dried formulation is always suitable for a frozen liquid and liquid formulation, but the inverse is not true. Therefore, end-in-mind development of a formulation that can be lyophilized, even if a liquid is used for phase 1 studies, results in overall faster timelines and lower risk.