Same Project, Different Start: How Contribution Events Shape Activity and Retention in Open Source

Open source projects depend on newcomers who stay, yet most leave after a single contribution. Contribution events such as Google Summer of Code, LFX Mentorship, Hacktoberfest, and 24 Pull Requests attract thousands of newcomers each year, but whether they produce lasting contributors remains unclear. We conduct the first matched-cohort study comparing 2,001 event-based and 2,001 organic contributors across 330 projects. Our results reveal three key findings. First, event contributors have significantly higher odds of becoming core contributors (12.1% vs. 9.6%, p < 0.001, OR = 1.31) and stay significantly longer (median 8.2 vs. 4.8 months). Second, each entry mechanism is associated with a fundamentally different engagement rhythm: 68.9% of mentorship contributors sustain Steady weekly activity across their first 12 weeks, whereas 61.0% of non-mentorship contributors exhibit Front-Loading and 57.0% of organic contributors exhibit Intermittent engagement (p < 0.001). Third, Steady engagement is associated with significantly longer retention regardless of group (median 13 vs. 8 months for Front-Loading), yet mentorship contributors who lose their program scaffolding show shorter retention than self-sustained non-mentorship contributors, revealing a mentor-dependency effect. A newcomer's first 12 weeks are strongly indicative of their long-term trajectory.