# Astro astro@6.4.0 — Release & Upgrade Intelligence
- **Product:** Astro (https://astro.build)
- **Version:** astro@6.4.0
- **Released:** May 28, 2026
- **Impact Score:** 5/10
- **Breaking Changes:** Not verified
- **Canonical Analysis:** https://changelogs.us/astro/updates/astro-6.4.0/

## Executive Summary (TL;DR)
Astro astro@6.4.0. Source highlight: Adds a new `preserveBuildServerDir` adapter feature

## New Features
- Adds a new `preserveBuildServerDir` adapter feature
- Adds a new `markdown.processor` configuration option, allowing you to choose an alternative Markdown processor.

## Bug Fixes
- Skips the static preview server when an adapter provides its own `previewEntrypoint`, allowing the adapter to handle both static and dynamic routes
- Fixes `X-Forwarded-Host` and `X-Forwarded-Proto` headers being ignored when set in a custom `src/app.ts` fetch handler before creating `FetchState`
- Fixes the static preview server to respect `preserveBuildClientDir`, serving files from `build.client` instead of `outDir` when the adapter requires it
- Fixes a race condition where the Vite dep optimizer could lose React dependencies in dev mode when using Astro Actions
- Exempts internal routes (e.g. server islands) from `getStaticPaths()` validation, fixing server island rendering on static sites
- Fixes preview for static sites that contain non-prerendered routes. Previously, the preview command ignored SSR routes discovered during route scanning and always used the static preview server.

## Upgrade Command
```bash
npm install --save-exact astro@6.4.0
```