Tailwind CSS v4 is a ground-up rewrite, and the performance numbers are the first thing you notice. The Oxide engine, written in Rust, processes stylesheets so fast that build times effectively disappear from your development workflow. A project with 50,000 utility class usages builds in under 100 milliseconds. Hot reload in development is instantaneous - there is no perceptible delay between saving a file and seeing the change.
The shift from JavaScript configuration to CSS-based @theme directives is the bigger philosophical change. Your design tokens - colors, spacing, fonts, breakpoints - now live in CSS where they arguably belong. This means your Tailwind configuration is portable, can be shared between projects as a CSS file, and works with any build tool without plugin configuration. The migration codemod converts most v3 configurations automatically, though custom plugins need manual attention.
New utility features include native container queries (no plugin needed), 3D transform utilities, improved gradient controls, and automatic dark mode that respects system preferences without configuration. The elimination of PostCSS as a requirement simplifies toolchain setup considerably. For new projects, you can use Tailwind v4 with just a CSS import - no config file, no PostCSS config, no build plugin. It just works with Vite, Next.js, or any other modern build tool out of the box.
Start new projects with Tailwind v4 for the performance gains, and run the migration codemod on existing projects when you have a free afternoon.
