The Problem
A DTC brand running on a heavily customized Dawn-derived Liquid theme was bleeding mobile conversions. LCP clocked at 4.2 seconds on 4G. The theme's JavaScript bundle bloated to 480 KB from accumulated app embed scripts. Every product page loaded synchronously, and the cart mutation round-trip averaged 1.8 seconds.
Architecture Decision
The migration followed a phased strangler-fig pattern. Phase 1: static PDPs moved to Hydrogen with ISR revalidation at 60-second intervals, served from Vercel Edge. Phase 2: the cart and checkout flow stayed on Liquid initially, then migrated to edge-rendered mutations via the Storefront API. Phase 3: ReCharge subscription management and Klaviyo email capture were re-implemented as React components with lazy hydration.
Performance Strategy
Every PDP is statically generated at build time from the Storefront API, then ISR-revalidated. The search experience switched from Shopify's native search to an Algolia index populated by a webhook on product create/update. The Hydrogen app ships 68 KB of JavaScript to the client — an 86% reduction. Cart drawer opens via a preloaded API call with optimistic UI, making the interaction feel instant.
Outcome
Mobile LCP dropped from 4.2s to 0.9s. Mobile conversion rate increased 22%. Overall revenue grew 18% within 60 days post-migration with no change to ad spend. The Hydrogen codebase is 40% smaller than the Liquid theme it replaced, with zero app-embed bloat.