Next.js 15.5 Release: Focuses on faster production builds, more powerful server-side middleware, and TypeScript improvements. It also warns developers about changes in Next.js 16.

• Turbopack: An incremental, Rust-based bundler replacing Webpack, used in Vercel applications. Can be opted into with next build --turbopack, showing 2x to 5x faster compilation times across project sizes. Built projects serve similar or less JavaScript and CSS with fewer requests.
• Stabilized Node.js Middleware Runtime: Allows middleware to run with full Node APIs, opening new patterns. NodeJS runtime not default in Next 16 but may be in future versions.
• TypeScript Improvements: Makes typed routes stable, introduces route export validation and helper types (PageProps, LayoutProps, and RouteContext), and adds a next typegen command.
• Linting Changes: Deprecates next lint command in favor of explicit linter configurations (ESLint or Biome). Automatic linting during builds will be removed in Next.js 16.
• Deprecation Warnings: Aims to smooth the jump to Next.js 16 by surfacing compile-time or build warnings for legacy items like legacyBehavior in next/link, AMP, and next/image behavior.