The new Curriculum for Wales seeks to develop young people who are ethical, informed citizens of Wales and the world and committed to the sustainability of the planet. While the curriculum requires the integration of subject knowledge, the associated guidance fails to suggest a philosophy of knowledge to inform such integration. Having linked sustainability to political economy and regimes of truth, rule and accumulation, this article draws on the Gesturing Towards Decolonial Futures Collective's typology of social reform spaces to consider spaces of sustainability politics in Wales. It then argues that the curriculum should enable students to articulate and contest sustainability within and across these spaces, a form of radical global citizenship education. Critical realism can guide curriculum delivery as it provides insights into inter-disciplinary enquiry, the role of critical pedagogy and the development of learners as non-dual beings who are at one with themselves and other human and non-human beings and thereby prepared to act as global citizens seeking sustainability.