While most β-decay studies focus on allowed decays to test the Standard Model, unique first-forbidden decays offer exceptional sensitivity to new physics. Several ongoing experiments aim to measure these decays with high precision, relying heavily on accurate theoretical predictions. I will present the first nuclear ab initio predictions for forbidden β-decays, incorporating several theoretical advancements, focusing on the decay of 16N which is currently being prepared for measurement at SARAF. I will then address broader theoretical challenges, particularly at the intersection of nuclear structure and radiative corrections, introducing an EFT analysis of expected contributions and their implications for the unique opportunities that upcoming forbidden decay measurements present for probing new physics.