# Astro astro@6.4.2 — Release & Upgrade Intelligence
- **Product:** Astro (https://astro.build)
- **Version:** astro@6.4.2
- **Released:** May 28, 2026
- **Impact Score:** 5/10
- **Breaking Changes:** Not verified
- **Canonical Analysis:** https://changelogs.us/astro/updates/astro-6.4.2/

## Executive Summary (TL;DR)
Astro astro@6.4.2. Source highlight: Fixes a `plugins is not iterable` crash when using a pre-6.0 `@astrojs/mdx` alongside integrations (e.g. Starlight) that set `markdown.remarkPlugins`, `markdown.rehypePlugins`, or `markdown.remarkRehype`.

## Bug Fixes
- Fixes a `plugins is not iterable` crash when using a pre-6.0 `@astrojs/mdx` alongside integrations (e.g. Starlight) that set `markdown.remarkPlugins`, `markdown.rehypePlugins`, or `markdown.remarkRehype`.
- Fixes an issue where on-demand (SSR) dynamic routes would return 404 when a prerendered dynamic route with the same URL pattern was sorted first alphabetically. In production builds with `@astrojs/node` adapter, if `[a_prebuild].astro` (prerender=true) came before `[b_ssr].astro` alphabetically, requests to URLs not in the prerendered route's static paths would 404 instead of falling through to the SSR route. The fix adds fallthrough logic so that when a prerendered dynamic route matches but can

## Upgrade Command
```bash
npm install --save-exact astro@6.4.2
```