Next.js 16.3 adds experimental controls over how Turbopack chunks JavaScript

Vercel published the reasoning behind Turbopack's chunking on September 3, 2026, with new experimental options in Next.js 16.3. generateComponentChunks emits un-merged chunks beside merged ones so the runtime can fetch whichever is cheaper given what the browser holds. firstPageLoadPriority, priorityRoutes and clusters replace Turbopack's assumption that two thirds of sessions are one page. turbopackSharedRuntime also cuts a blocking request and about 10 KB per navigation.

Why it matters

Chunking defaults are a guess about how people move through a site, and the post says so plainly: the two-thirds weighting is an estimate. If you have analytics, you know better than the default does, and this is the first release that lets you say so.

Who should care

Next.js teams tuning page weight and navigation speed

What you can do

Set firstPageLoadPriority from your actual bounce rate and list your genuinely hot routes in priorityRoutes, then measure requests and transferred JavaScript either side of the change.