This paper addresses the role of incumbent firms in driving transitions that entail multiple sectors, conditioned by multiple regimes. We analyse the case ‘HYBRIT’, a radical innovation venture championed by three incumbents from the steel and energy regimes. We investigate what conditions the incumbents’ agency and how they enacted their agency targeting restructuring of the regime elements–actors, institutions, and materiality. We find that eight endogenous and exogenous factors coincide and condition the incumbents’ agency, from which they act in a novel direction of change. We contribute by showing how the collaboration within and across regimes enabled the accomplishment of actions that would have been challenging for individual incumbents to achieve alone. In this setting of scale-intensive industries, incumbents have characteristics that give them a significantly larger capacity to stimulate change than newcomers. The timing and combination of endogenous and exogenous factors, enabling incumbents to collectively drive a transition. © 2024 Informa UK Limited, trading as Taylor & Francis Group.