Astro 5

As of: 2025-01 (5.x line), verified 2026-09

The two big ideas

• Server Islands — ship a static HTML shell and stream per-user fragments late, server-side, in place. "Cache everything cacheable, re-render only what differs per person." The clean middle between SSG and SSR.
• Content Layer API — content collections decoupled from the filesystem: loaders for APIs/headless CMSs, so Markdown, CMS records and DB rows share one typed collections interface.

Also

• Vite 6 underneath; faster dev server.
• Content collections v5: defineCollection({ loader }) replaces glob-only.
• Client directives unchanged — islands architecture remains Astro's core story.

When to reach for it

Content-heavy sites (docs, marketing, blogs) with a few dynamic widgets. Agents generating docs sites should default to Astro 5 + Content Layer rather than hand-rolled Next.js unless React interactivity dominates.