Juxtaposing two local council cases of open source software adoption in the UK we highlight their differences and similarities in open source adoption and implementation. Our narratives indicate that for both cases there was strong goodwill towards open source yet the trajectories of implementation differed widely. We draw on Deleuze and Guattari’s ideas of becoming, tracing versus mapping and multiplicity to explain how becoming occurs at different speeds. Our data shows that the becoming of adoption can be both constrained and precipitated by various forms of materiality (of the assemblage of the open source ecosystem). The interesting point of departure of our study is how open source software – a much touted transparent and open phenomenon – is by its nuanced and layered mutability able to make the process and practices surrounding it less visible.