Around 2009–2010, opening up public data was a governmental strategy in the UK, as part of the implementation of the Transparency Agenda, based on the assumption that unfettered access to government data would inexorably lead to transparency, accountability and participation. Following this conjecture, and in an attempt to create an alternative to the corporate-driven smart city discourse, the Greater London Authority prioritised open data in its initial smart city plans to facilitate a ‘citizen-centred’ smart city. However, subsumed within the digital economy, open data was eventually promoted and implemented primarily for its lucrative potential to create new businesses, rather than prioritising the aspirations of transparency and participation. In this article, I explore the implications of this shift and the nature of open data- driven smart city making by focusing on a transport app, Citymapper that is built on open data released by Transport for London (TfL). By closely studying the app's product development process to generate profit together with its struggle to raise funding through venture capital and crowdfunding, I arrive at two main arguments. First, I argue that open data driven smart city making in London was a form of experimentation instead of a formal and rigid planning as it saw open data as an end in itself without much understanding of what this process would lead to in practice. As such, the case of Citymapper shows that the contingent process of opening up public transport data meant opening up public infrastructure in the city. Second, by examining the app's unsustainable business models and detailing its struggle to maintain revenue and profitability, I outline how open data-driven products are ultimately subsumed within the logic of platform capitalism rather than creating an alternative digital economy.