This study investigates treatments for Ulcerative Colitis, a condition characterized by long-lasting inflammation and sores in the lining of the large intestine. The purpose of the study is to evaluate the effectiveness of combining two different medicines compared to using just one. The medications being studied include mirikizumab, which is given through intravenous injection (delivered directly into a vein) or subcutaneous injection (delivered just under the skin), and LY4268989, which is an oral capsule. Some participants may also receive a placebo.

During the study, participants will be assigned to different groups to receive either the combination of LY4268989 and mirikizumab or mirikizumab alone. The process is double-blind, meaning neither the participants nor the researchers know which specific treatment is being administered. The course of the study involves monitoring the participants over a 12-week period to observe how they respond to the medications.