A five-week in-person technical training program in machine learning engineering for AI safety, run at the London Initiative for Safe AI (LISA) in Shoreditch, London, with an optional opening week reviewing neural network fundamentals. ARENA is fully funded: travel to and from London, visa expenses, accommodation for the full duration, and meals on programme days are all covered. Applicants need solid Python and the mathematics behind modern machine learning (linear algebra, calculus, probability) plus a clear view of how they want to contribute to technical AI safety. Cohorts run several times a year; alumni have gone on to research roles and to programs such as MATS.