We study how a rivalrous interorganizational relationship transforms into a coopetitive strategy. The study employs a qualitative method and systematic combining approach to examine an evolving coopetitive relationship in the truck industry. We studied a platform project during the concept phase of development. We found that multibrand platform development is characterized by innovation barrier multiplicity and concurrency. The study presents a model where we propose that history-related Initial Conditions Innovation Barriers (ICIB) are blended with project-related Emerging Innovation Barriers (EIB). This research makes a theoretical contribution by proposing that through strategic and operational stretch firms transform from a homogenous competitive relationship to a heterogeneous coopetitive relationship.