The goal of the NANO trial is to study the longstanding clinical practice of empirically administering intravenous antibiotics to extremely low birthweight (ELBW) infants in the first days of life. In this 802-subject multicenter placebo-controlled randomized clinical trial, the hypothesis to be tested is that the incidence of adverse outcomes is higher in babies receiving empiric antibiotics (EA) in the first week of life compared to babies receiving placebo. The study targets a population of ELBW infants in whom the clinical decision to use or not use EA is currently most challenging -- infants that are clinically stable that did not have a known exposure to intraamniotic infection and were not born preterm for maternal indications. The primary outcome is the composite outcome of late-onset sepsis (LOS), necrotizing enterocolitis (NEC), or death during the index hospitalization. Secondary safety outcomes will include total antibiotic days, days to full enteral feedings, and common morbidities in preterm infants that have previously been linked to EA, e.g. retinopathy of prematurity and bronchopulmonary dysplasia. Weight and length z-score, and head circumference, are standard measures to be collected weekly by clinical team per a standardized protocol.