Purpose The XELAVIRI trial investigated the optimal treatment strategy for patients with untreated metastatic colorectal cancer. We tested the noninferiority of initial treatment with a fluoropyrimidine plus bevacizumab, followed by the addition of irinotecan at first progression (arm A) versus upfront use of fluoropyrimidine plus irinotecan plus bevacizumab (arm B) in a 1:1 randomized, controlled phase III trial. Methods The primary efficacy end point was time to failure of the strategy (TFS). Given a 90% CI, a power of 70%, and a one-sided α of .05, the margin for noninferiority was set at 0.8. In the case of demonstrated noninferiority of TFS, an analysis of symptomatic toxicities during TFS would define the superior strategy. Secondary end points included the effect of molecular subgroups on efficacy parameters. Results A total of 421 randomly assigned patients (arm A: n = 212; arm B: n = 209) formed the full analysis set. Median age was 71 and 69 years, respectively. Noninferiority of TFS was not shown (hazard ratio [HR], 0.86; 90% CI, 0.73 to 1.02). In detail, patients with RAS/BRAF wild-type tumors benefitted from combination chemotherapy (HR, 0.61; 90% CI, 0.46 to 0.82; P = .005), whereas patients with RAS mutant tumors (HR, 1.09; 90% CI, 0.81 to 1.46; P = .58) did not (Cox model for interaction of study arm and RAS status: P = .03). Comparable results were obtained for overall survival. Conclusion Noninferiority of sequential escalation therapy compared with initial combination chemotherapy could not be demonstrated for TFS. RAS status may be important to guide therapy as treatment of patients with upfront combination therapy was clearly superior in RAS/BRAF wild-type tumors, whereas sequential escalation chemotherapy seems to provide comparable results in patients with RAS mutant tumors.