Tailwind v4 (January 2025) — Oxide engine; CSS-first @theme config; ~3.5× faster full builds, ~8× faster incrementals

Claim: Tailwind v4 released January 2025. Per Tailwind Labs' Catalyst-project benchmark (tailwindcss.com/blog/tailwindcss-v4): "full rebuilds to be over 3.5x faster, and incremental builds to be over 8x faster"; median full build dropped from 378ms to 100ms; "incremental builds that don't actually need to compile any new CSS — these builds are over 100x faster and complete in microseconds."

Confidence: Verified for the qualitative finding (substantially faster, microsecond no-op incrementals); exact multiplier varies by project shape.

Key changes:

• Oxide engine (Rust-based).
• CSS-first config via @theme directive — no more tailwind.config.js.
• Native cascade layers (@layer).
• Auto content detection — no more content array.

For Candid: standardize Tailwind v4 with @theme config on every new project. Do not migrate existing v3 projects retroactively — 4-8 hours per project with custom plugins. Adopt-for-new is the right policy.

Counter-position worth holding: for static marketing sites with a strong bespoke design system, hand-written modern CSS (nesting + container queries + @scope + custom properties + light-dark()) is now genuinely viable and ships smaller. Take this position on projects where the design is highly bespoke.