Heap's transition from CoffeeScript to TypeScript began over four years ago, driven by a renewed effort in 2019 to address the slow migration pace and lack of momentum in achieving a 100% TypeScript codebase. The company realized that successful tech stack migrations are as much about people as technology, emphasizing the importance of developer buy-in and the necessity of making the switch to TypeScript appear as a productivity enhancement rather than a mere syntactic shift. Strategic codebase conversion, improved tooling, and configuration were employed to bolster productivity, while breaking down technical barriers and simplifying the conversion process ensured a seamless transition. Automation tools like decaffeinate helped facilitate the migration, and a dedicated Slack channel offered support and expertise to developers, fostering a collaborative environment. Progress was tracked using visualization tools, underscoring the importance of gradual improvement over perfection. Leadership played a crucial role by allowing engineers the autonomy to drive the project, which was internally motivated and executed. The ongoing learning from this migration aims to inform future technical transitions, all while inviting new talent to join Heap's engineering team.