Next.js Knowledge Patch (15.3 – 16.x)

Supplementary knowledge for Next.js features released after Claude's training cutoff. Covers versions 15.3 through 16.1 (April 2025 – January 2026).

Request Interception: proxy.ts

Next.js 16 replaces middleware.ts with proxy.ts. Rename the file and export a proxy function instead of middleware. Runs on Node.js runtime by default.

// proxy.ts (project root)
import { NextRequest, NextResponse } from 'next/server';

export function proxy(request: NextRequest) {
  return NextResponse.next();
}

middleware.ts still works (Edge runtime) but is deprecated and will be removed.

15.5 note: Middleware gained stable Node.js runtime support via export const config = { runtime: 'nodejs' } before the full proxy.ts transition.

Caching: "use cache" and Cache Components

Next.js 16 introduces an opt-in caching model. All dynamic code runs at request time by default — caching is no longer implicit. Enable with:

// next.config.ts
const nextConfig: NextConfig = {
  cacheComponents: true,
};

Apply the "use cache" directive to cache pages, components, or functions. The compiler generates cache keys automatically:

'use cache';

export default async function CachedPage() {
  const data = await fetchData();
  return <div>{data}</div>;
}

Replaces experimental.ppr and experimental.dynamicIO. Completes the Partial Prerendering story — static shells with dynamic holes via Suspense, fully opt-in.

For detailed caching API patterns and code examples, see references/caching.md.

Caching API Quick Reference

API	Context	Semantics	Use Case
updateTag(tag)	Server Actions only	Read-your-writes (immediate)	Forms, user settings
refresh()	Server Actions only	Refreshes uncached data only	Notification counts, live metrics
revalidateTag(tag, profile)	Any server context	SWR (eventual consistency)	Static content invalidation

Breaking: revalidateTag() now requires a cacheLife profile as 2nd argument ('max', 'hours', 'days', or { expire: N }).

Navigation Hooks (15.3+)

onNavigate — prop on <Link>. Fires during SPA navigations only (not all clicks). Call e.preventDefault() to cancel.

<Link
  href="/dashboard"
  onNavigate={(e) => {
    if (hasUnsavedChanges) e.preventDefault();
  }}
>
  Dashboard
</Link>;

useLinkStatus — hook from next/navigation. Returns { pending: boolean }. Must be used inside a <Link> descendant. Modeled after React's useFormStatus.

'use client';
import { useLinkStatus } from 'next/navigation';

function LinkSpinner() {
  const { pending } = useLinkStatus();
  return pending ? <Spinner /> : null;
}

// <Link href="/page"><LinkSpinner /> Go</Link>

TypeScript (15.5+)

Route Props Type Helpers

Auto-generated PageProps, LayoutProps, RouteContext types — globally available, no imports needed:

// app/blog/[slug]/page.tsx — no manual typing needed
export default async function Page({ params }: PageProps) {
  const { slug } = await params;
  return <article>{slug}</article>;
}

Typed Routes

Compile-time route validation — moved from experimental to stable:

// next.config.ts
const nextConfig: NextConfig = { typedRoutes: true };

Invalid <Link href> paths cause TypeScript errors. Works with both Webpack and Turbopack.

next typegen

Standalone type generation for CI validation without running dev/build:

next typegen && tsc --noEmit

File Conventions

File	Since	Purpose
proxy.ts	16.0	Request interception (replaces middleware.ts)
instrumentation-client.js|ts	15.3	Client-side monitoring/analytics — runs before app code
default.js in parallel routes	16.0	Required for all slots or build fails

Configuration Reference

Config	Purpose	Since
cacheComponents: true	Enable "use cache" + PPR	16.0
reactCompiler: true	React Compiler (was experimental)	16.0
typedRoutes: true	Typed routes (was experimental)	15.5
turbopack: { ... }	Turbopack config (was experimental.turbo)	15.3
Turbopack is default bundler	Opt out with --webpack flag	16.0

Removed config: experimental.ppr, experimental.dynamicIO, serverRuntimeConfig, publicRuntimeConfig (use .env files), devIndicators options.

Tooling Changes

• next lint removed (16.0) — use ESLint CLI or Biome directly. Codemod: npx @next/codemod@latest next-lint-to-eslint
• next typegen (15.5) — standalone type generation for CI
• Turbopack FS caching — stable and on by default for next dev in 16.1

React 19.2 (via App Router, 16.0+)

These are React-level APIs available through the App Router's React Canary channel. Refer to the React 19.2 docs for full usage details.

• <ViewTransition> — animate elements during transitions
• useEffectEvent() — extract non-reactive logic from Effects into stable functions
• <Activity> — hide UI (display: none) while preserving state and cleaning up Effects

Breaking Changes (16.0)

For full migration details with code examples, see references/migration-guide.md.

• Node.js 20.9+, TypeScript 5.1+, Chrome/Edge/Firefox 111+, Safari 16.4+
• Async APIs enforced: await params, await searchParams, await cookies(), await headers() — sync access now errors
• Parallel routes: all slots require explicit default.js or build fails
• Removed: AMP, next lint, legacyBehavior on Link, serverRuntimeConfig/publicRuntimeConfig
• Image defaults: images.qualities → [75], minimumCacheTTL → 14400s, localPatterns required for query strings, dangerouslyAllowLocalIP blocks local IPs

Additional Resources

Reference Files

• references/caching.md — Detailed "use cache", updateTag(), refresh(), revalidateTag() patterns with code examples
• references/migration-guide.md — Complete Next.js 16 breaking changes, removals, and migration steps