Next.js, a popular web development framework, has just released its version 15 Release Candidate (RC). This early version gives developers a chance to test out the latest features before the stable release.

First off, Next.js 15 RC now supports React 19 RC, which includes new features for both the client and server side. It also introduces an experimental React Compiler that can automatically optimize your code, making it simpler and less error-prone.

Another improvement is in the handling of hydration errors. Next.js 15 displays the source code of the error along with suggestions on how to fix it, making debugging a breeze.

Next.js has also made changes to its caching defaults. Fetch requests, GET Route Handlers, and Client Router Cache are no longer cached by default. However, you can still opt into caching when needed.

Partial Prerendering (PPR), introduced in Next.js 14, gets an update too. You can now incrementally adopt PPR in specific Layouts and Pages using a new route configuration option.

A new experimental API called next/after allows you to execute code after a response has finished streaming. This is useful for tasks like logging or analytics that shouldn't block the main response.

create-next-app, the tool used to set up a new Next.js project, got a design update and a new flag to enable Turbopack, a high-performance bundler, during local development.

Lastly, Next.js 15 introduces a new configuration option to optimize the bundling of external packages, improving the cold start performance of your application.