Next.js 15: What's New and How to Upgrade

Next.js 15 is here, and it's a significant release that brings performance improvements, new APIs, and a better developer experience. As a team that builds exclusively with Next.js, we've been testing these features extensively. Here's what you need to know.

Key Features in Next.js 15

Async Request APIs

One of the biggest changes in Next.js 15 is the shift to async request APIs. Previously synchronous functions like cookies(), headers(), and params are now asynchronous. This is a breaking change, but it enables better performance by allowing the framework to optimize rendering more effectively.

React 19 Support

Next.js 15 ships with React 19 support, bringing Server Components out of the canary channel and into stable. This means better streaming, improved suspense boundaries, and the new use hook for simpler data fetching patterns.

Turbopack Stable

Turbopack, the Rust-based successor to Webpack, is now stable for development. In our testing, dev server startup is 76% faster, and Fast Refresh is 96% faster. For large codebases, this is a game-changer.

How to Upgrade Your Existing Project

Upgrading requires attention to a few key areas:

• Update dependencies: Bump next, react, and react-dom to their latest versions
• Async params: All params and searchParams props are now Promises — you must await them
• Caching changes: fetch requests and Route Handlers are no longer cached by default — be explicit about your caching strategy
• Test thoroughly: Use the built-in codemod (npx @next/codemod@canary upgrade latest) to automate most changes

Should You Upgrade Now?

If you're starting a new project, absolutely use Next.js 15. If you have an existing production app, test the upgrade in a staging environment first. The async API changes can introduce subtle bugs if not handled carefully.

At VertexWave, all new projects already use Next.js 15, and we're actively upgrading existing client sites. The performance gains — especially from Turbopack — are well worth the migration effort.