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Experimental SSR Streaming

Flush the HTML shell immediately and stream the body as Vue renders — a big Time to First Byte win for content-heavy routes. With the gotchas that matter.

Source: PR #1

What's new#

Nuxt 4.5 adds experimental SSR streaming: instead of buffering the whole page and sending it in one shot, Nuxt flushes the HTML shell (your <head>, styles, preload hints, entry scripts) right away, then streams the body as it renders.

Why you'd care#

Time to First Byte (TTFB) drops dramatically for content-heavy routes, because the browser starts receiving and painting the page immediately. Bots and crawlers still get fully-rendered HTML — streaming is disabled for them automatically.

Before#

Everything was buffered and sent as one response:

nuxt.config.ts
export default defineNuxtConfig({
  // default: whole page buffered, then sent
})

The user's browser waited for the entire render to finish before receiving the first byte.

After#

Turn it on experimentally:

nuxt.config.ts
export default defineNuxtConfig({
  experimental: {
    ssrStreaming: true,
  },
})

Tune which user agents count as crawlers, and opt individual routes out:

nuxt.config.ts
export default defineNuxtConfig({
  experimental: {
    ssrStreaming: {
      botRegex: /googlebot|bingbot|my-internal-crawler/i,
    },
  },
  routeRules: {
    '/no-stream/**': { streaming: false },
  },
})

Do it yourself#

  1. Add experimental: { ssrStreaming: true } to nuxt.config.ts.
  2. Build and preview a content-heavy route (e.g. a long blog post).
  3. In the Network tab, confirm the response streams rather than arriving all at once (you'll see bytes arriving over time).
  4. Add a /no-stream/** route rule and confirm that route falls back to buffered rendering.
  5. Test a setResponseStatus() in a page script to see the dev warning about dropped mutations.

Gotchas#

This is the big one. Because the HTTP status and headers commit with the first byte, anything that mutates the response after rendering has begun — setResponseStatus() in <script setup>, cookie writes in middleware — can't reach the client. Nuxt auto-falls back to the buffered renderer for routes with redirect, cache, isr, swr, noScripts, or ssr: false rules, and logs a dev warning naming any dropped mutations. Audit your response-mutating logic before shipping widely.

Recap#

experimental.ssrStreaming flushes the shell first for big TTFB wins; bots get full HTML; mutating status/headers/cookies after streaming starts is dropped (with a dev warning). Test against your response logic first.

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