In Part B, participants with hepatitis C virus (HCV) GT1 and HCV ribonucleic acid (RNA) levels of ≥10,000 IU/mL will be randomly assigned to a study arm, based on absence or presence of cirrhosis (C), whether they are TN or had poor response to previous antiviral therapy (null responders [NR]), or whether co-infected with human immunodeficiency virus (HIV); these participants will receive open-label grazoprevir (100 mg) in combination with elbasvir (50 mg) ± RBV. Treatment will last 8 to 18 weeks dependent on arm assignment.