Next.js 15.5: Turbopack Builds, Node.js Middleware, and TypeScript Superpowers

Next.js 15.5 is a milestone release that brings Turbopack builds to beta, stabilizes Node.js middleware, and introduces powerful TypeScript enhancements. It also begins phasing out legacy features in preparation for Next.js 16.

⚡ Turbopack Builds (Beta)

Turbopack, the Rust-based successor to Webpack, is now available for production builds via next build --turbopack.

• Powers major Vercel sites like vercel.com and nextjs.org

• Delivers up to 5x faster builds on large projects

• Uses multi-core compilation for scalable performance

• Still being refined for bundle optimization and CSS ordering

🧩 Node.js Middleware (Stable)

Middleware now supports the Node.js runtime natively, allowing access to:

• File system (fs)

• Cryptography (crypto)

• Complex auth logic and third-party libraries

This unlocks richer middleware capabilities beyond the Edge runtime, though Edge remains the default for now.

🧠 TypeScript Improvements

Next.js 15.5 supercharges the App Router with:

• Typed Routes: Compile-time validation for <Link> paths

• Route Export Validation: Type guards for layouts and handlers

• Auto-generated Props: PageProps, LayoutProps, and RouteContext now available globally

• New CLI: next typegen for manual type generation and CI validation

🧼 Linting Overhaul

The next lint command is deprecated. Instead:

• Projects now use explicit ESLint configs or Biome

• Scripts like "lint": "eslint" or "lint": "biome check" replace the wrapper

• A codemod helps migrate existing setups seamlessly

⚠️ Deprecation Warnings for Next.js 16

To ease the transition, Next.js 15.5 introduces warnings for features that will be removed in v16:

• legacyBehavior in <Link>

• AMP support (useAmp, amp: true)

• quality prop in <Image> (restricted to 75 unless configured)

• Local image paths with query strings (require images.localPatterns)

🏁 Final Thoughts:

Next.js 15.5 isn’t just a performance upgrade—it’s a strategic pivot toward a more scalable, type-safe, and developer-controlled future. With Turbopack builds, Node.js middleware, and smarter linting, it lays the groundwork for Next.js 16 and beyond.