Human-intensive programs like teacher mentoring face a fundamental scaling problem: evidence shows their impact declines as they expand, and the personalized support that makes them effective becomes prohibitively expensive at scale. This paper explores whether AI-powered tools can help resolve this tension. We document the development and pilot implementation of ”Profe Gabi,” a generative AI chatbot designed to provide novice teachers in Chile with on-demand mentoring support through WhatsApp. The chatbot delivers personalized guidance across three dimensionspedagogical practice, socio-emotional well-being, and career developmentdrawing on Chiles existing National Induction and Mentoring System, which currently reaches fewer than 1% of eligible teachers due to capacity constraints. During an eight-week pilot with 550 novice teachers, Profe Gabi demonstrated the technical feasibility of scaling mentoring support: it reached more than three times the number of teachers served by the national program while maintaining high user satisfaction. However, engagement declined significantly, revealing critical implementation challenges around sustained adoption. We analyze these patterns to identify what conditions may be necessary for AI tools to meaningfully expand access to professional development, and discuss insights that inform Profe Gabis scale-up in 2025-2026. Our study contributes to an emerging literature on AI technologies for teacher support and offers lessons for similar interventions globally