How Millions Coordinate at Scale: Engagement, Collaboration, and Conflict in Three Editions of Reddit r/place

Mass peer-production environments are shaped by a complex interplay between decentralized coordination, platform design, and potential conflict over resources. While online infrastructures enable large-scale collaboration, they can also introduce coordination challenges and contested interactions among participants. The Reddit r/place experiment provides a unique socio-technical setting for studying these dynamics across three distinct editions (2017, 2022, and 2023). By allowing millions of participants to collaborate and compete as they update pixels on a finite shared digital canvas, the events generated fine-grained traces comprising hundreds of millions of actions taken over multiple days. In this paper, we examine how participation, collaboration, and conflict evolve within r/place. First, we conduct a longitudinal, cross-edition analysis of engagement and collaboration patterns across the 2017, 2022, and 2023 events. Second, to investigate collaborative activity beyond surviving final artifacts, we introduce a scalable graph-based dynamic clustering framework and apply it to the 2017 event to reconstruct coalition trajectories from behavioral interaction logs, enabling the analysis of both persistent and transient efforts. Our findings reveal recurring organizational patterns across editions: participation remains highly concentrated to few participants despite individual rate-limiting constraints, larger coalitions exhibit both greater coordination inefficiencies and lower median per-participant activity, while still success increasingly concentrates within large collaborative groups over the course of an event. Analysis of recovered coalition trajectories further shows that coalition outcomes are difficult to predict based on state characteristics during much of the event, highlighting the dynamic and contested nature of collaborative production in r/place.