The US Food and Drug Administration issued draft guidance recommending comparative analytical assessments (CAAs) as the primary route to demonstrate biosimilarity, advising that comparative efficacy studies (CES) be dropped for most products. Biosimilar industry groups broadly welcomed the shift but asked FDA to spell out when CES remain necessary. Innovator trade group PhRMA pushed back, arguing CES should be retained for complex modalities such as multi‑specific antibodies and antibody‑drug conjugates. Stakeholders told FDA in public comments that making CAAs the default would speed biosimilar development and reduce clinical burdens, but multiple respondents asked for clearer decision criteria and examples. The debate matters because the agency’s default approach will reshape development costs, trial design and market entry timelines for a growing wave of complex biologics.