The Lean Startup method advises new ventures to prioritize early customers as they build their first products. However, it remains less clear how this approach works in highly regulated environments, where multiple actors, beyond early customers, have significant influence determining acceptable product attributes and business models. To explore how new ventures build their first products in a highly regulated environment, we use a comparative case study of two fintech ventures entering the Australian banking industry. We find that instead of closely following the Lean Startup, the ventures chose paths that exhibited variation in overlap with only its “lean” resource ethos. One venture started close to a “lean” ethos by renting their assets, yet surprisingly, this led to limited learning and constraints that foreclosed strategic options. In contrast, a second venture began more distant to a “lean” ethos by building their assets. Despite high costs and early constraints, this path provided growth opportunities and greater strategic flexibility. Our study contributes to research on Lean Startup by demonstrating the alternative ways that a “lean” approach emerges in multi-actor environments, and to research on entrepreneurship in regulated environments, by highlighting the role of regulators in influencing new ventures’ early product decisions.