Fairness set and forgotten: Mining fairness toolkit usage in open-source machine learning projects

The development of machine learning (ML) systems in high-stakes domains has amplified concerns about fairness, prompting the creation of fairness toolkits offering metrics and mitigation techniques. Open-source software (OSS) ecosystems, a critical driver of AI innovation, present a unique opportunity to study the practical adoption of these toolkits. This paper aims to empirically characterize the adoption of fairness toolkits in OSS ML projects by investigating for what purposes they are used and how their usage evolves over time. We conducted a mining study on GitHub repositories related to real-world ML projects that integrate fairness toolkits such as AIF360 and Fairlearn . Starting from 1,096 candidate repositories, we applied systematic filtering to identify a final dataset of 20 relevant ML projects (comprising 5,777 total commits). We analyzed toolkit usage by examining invoked APIs and commit histories to uncover patterns of adoption and evolution. Our findings reveal that fairness toolkits are predominantly used for diagnostic purposes, with analytic components integrated early in the project lifecycle and rarely modified thereafter. In contrast, mitigation techniques are infrequently adopted, tend to appear later, and exhibit short, unstable lifespans. Our results show that the adoption of fairness toolkits in OSS ML projects is limited and often restricted to initial diagnostic phases, with active mitigation practices remaining rare. These findings highlight the need for improved support to foster more sustained and effective integration of fairness practices within open-source development.