Onboarding is a process of organizational socialization of the new hires, that includes recruitment, orientation, training, coaching and support. While onboarding individuals into an existing organization is a rather straightforward task, little is known about 1) onboarding hundreds of new developers and 2) doing it on a distance in outsourcing situations. Further-more, the subject of sustainable growth with respect to organizational capa-bilities and culture is often overlooked. This article reports findings from an exploratory multi-case study of two large onboarding campaigns. We collected empirical data from individual and group interviews, retrospec-tives, onboarding documentation and onsite visits to the onboarded com-panies. Based on the empirical study, onboarding hundreds of software en-gineers in a complex agile product development environment which lacks documentation and puts high demands on engineers’ knowledge and skills is a challenging and costly endeavor. To save the costs and for other practi-cal reasons, large-scale onboarding is organized in batches with the first batch trained onsite, and the later batches receiving the training internally. We report the challenges faced in the two cases and discuss possible solu-tions to address them. One core finding is that a good plan combined with the organizational agility, i.e., the responsiveness to change, together with organizational maturity determined the success of organizational scaling. The presented cases contribute to the scarce research on knowledge transfer and onboarding in a large-scale agile context.