Kasia Jastrzebska

What does it take to rebrand a massive, legacy codebase without breaking everything—or everyone? Join me on a storytelling journey through Cleo’s rebrand: a 7+ year old financial app built in React Native, layered with AI-powered chat, budget tools, and a credit-building card.This talk is a candid, practical case study on how we tackled technical debt, an inconsistent design system, webviews lurking in corners, and the sheer scale of a complex product. You'll hear how we gathered data, unified design tokens, incentivized adoption across squads, and introduced automation to prepare for the ultimate challenge: running a bold A/B test of two entirely different brand experiences—at scale.Whether you're dealing with a legacy app or planning a design system refresh, this talk offers actionable insights on navigating change in large mobile apps, while keeping your team and user experience intact.

Introducing design system into mature codebase. Let me walk you through our challenges, very useful tools to understand your current situation, tools to measure the impact of design system work, tools to make it happen.