The concept of ‘infrastructure’ is gaining purchase of late as an empirical and analytical locus for social theory. Its rise has coincided with both the empirical proliferation of new interface, media and digital sensor networks and an analytical sensibility that attends to the complex, adaptive and emergent processes that lend epistemic continuity and/or sustainability to social and biotic systems. Thus, there seems to be growing consensus that the functional and ontological dimensions of such self-organized systems are assembled together as relational ecologies. This talk looks at the work of open-source guerrilla architectural collectives in Madrid and their involvement in the sustenance of one such urban ecology. Open-source architecture presents a challenge to urban systems, however, insofar as it unsettles the current material, legal, technical, and socio-political conceptions of how infrastructures work. Opening the ‘source’ of an architectural project involves both making its designs available and re-sourcing its social and infrastructural capacities. That is, architectural collectives struggle to think and open anew – whilst simultaneously standardizing technical and documentary legacies, as well devising pedagogies about – what and where the ‘sources’ of a project might lie: its technical design systems, legal ritual, collaborative dynamics, governance mechanisms, materials and resources, or social and political capacities. Such an ecology of open sources has little time for conventional notions of knowledge, description, epistemology or ontology. Sources constantly re-source themselves, now as materials, now as media or iconographies, code, language, infrastructures, public spaces, archives, persons, collectives, etc. The ecology is therefore always and everywhere a ‘beta’ version of itself. The talk concludes with a meditation about anthropology itself entering the ecology of sources, and the larger implications of devising and working with conceptual infrastructures in beta, in the city and beyond.