What changed about caching defaults in Next.js 15?

Q: What changed about caching defaults in Next.js 15?

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity. **Difficulty:** Hard > **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified block names the version it ran on. ## 1. Why This Even Matters — A Story First Next.js 14 was a waiter who assumed you wanted "the usual" and kept bringing yesterday's dish unless you said otherwise. Many teams were surprised by stale data. Next.js 15 changed the waiter: now you get it fresh unless you ask for the usual. The food is the same, but the default question flipped, and after an upgrade you have to tell the waiter which dishes really should be "the usual". ## 2. The Core Idea 📌 **Interv

The problem

Question presented to candidate: "You are upgrading an app from Next.js 14. Which caching defaults changed in 15, what will you notice, and how do you opt back in where you need to?"

What a strong answer should cover:

fetch requests are no longer cached by default: the default moved from force-cache to not cached.
GET Route Handlers are no longer cached by default; opt in with export const dynamic = 'force-static'.
The client Router Cache no longer reuses pages of dynamic routes on navigation: staleTimes.dynamic went from 30 s to 0 s.
Static pages, layouts, loading states and back/forward navigation are still reused.
Next.js 16 keeps these defaults and adds Cache Components, where data is uncached unless marked with 'use cache'; since 16.4, create-next-app enables it for new App Router apps.

Clarifying questions expected:

"Which pages relied on implicit caching?" — they may get slower or hit the API more after the upgrade.
"Are you planning to adopt Cache Components?" — then opt back in with 'use cache' rather than fetch options.

Code / implementation expected: Yes — the three opt-backs.

nextjs
caching
next-15
defaults

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity. Difficulty: Hard

How to read this doc: Each idea is explained in plain language first, then tagged with 📌 Interview term:. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the Verified section, against real output from a build or a running server; each Verified block names the version it ran on.

1. Why This Even Matters — A Story First

Next.js 14 was a waiter who assumed you wanted "the usual" and kept bringing yesterday's dish unless you said otherwise. Many teams were surprised by stale data. Next.js 15 changed the waiter: now you get it fresh unless you ask for the usual. The food is the same, but the default question flipped, and after an upgrade you

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4 min read · 8 sections

Read the code

Opting back in, one place at a time

// 1. a fetch that may be reused
const data = await fetch("https://api.example.com/countries", { cache: "force-cache" });

// 2. a GET Route Handler served from the build output
// app/api/countries/route.ts
export const dynamic = "force-static";
export async function GET() {
  return Response.json(await getCountries());
}

// 3. the client cache lifetime for dynamic pages
// next.config.ts
const nextConfig = { experimental: { staleTimes: { dynamic: 30 } } };
export default nextConfig;

Discussion

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