Retrospective: Adopting Svelte 5 for Our Component Library – 30% Smaller Bundle Size and Faster Development

At our company, we maintain a shared component library used across 8+ frontend products, powering everything from internal dashboards to customer-facing web apps. For the past two years, the library has been built with Svelte 4, and while it served us well, we started hitting pain points as the library grew to 120+ components: bundle bloat, verbose reactivity boilerplate, and slower development cycles for new components.

When Svelte 5 launched with its reworked reactivity system (runes), smaller runtime, and improved compiler optimizations, we knew it was time to evaluate a migration.…