GitHub finished moving github.com off styled-components, and two engineers with Copilot agents cleared the last 895 sx props in three weeks
GitHub Blog·medium signal
Moving the Primer components to CSS Modules cut server-side render time 55% and component initialization 25%. The sx prop count peaked at about 7,760 in April 2025. A codemod and a VS Code plugin handled 6,419 props over six months, then Copilot coding agents cleared the long tail by June 2026 for per-page SSR gains of 1-22%. That split shows where a codemod stops paying and agents take over in a large migration.