Traditional approaches to K-anonymity provide privacy guarantees over publicly released data sets with specified quasi-identifiers. However, the most common public releases of personal data are now done through social networks and their APIs, which do not fit the previous research-centric data set release model, nor do they allow for clear assumptions about quasi-identifiers. This paper proposes a new definition of K -anonymity that suggests a practical way in which social networks could provide privacy guarantees to users of their API. To support as wide a range of applications as possible, the proposed privacy guarantee assumes all social-networking data may be a quasi-identifier and does not assume that data may be generalized and still be useful. Using the Facebook social networking API, we implement an application to demonstrate that providing such guarantees in real-time is feasible for real social networking data.