withastro · florian-lefebvre · Oct 1, 2025 · Sep 30, 2025 · Oct 1, 2025 · Oct 1, 2025
diff --git a/src/content/docs/en/guides/upgrade-to/v6.mdx b/src/content/docs/en/guides/upgrade-to/v6.mdx
@@ -279,6 +279,74 @@ const integration = () => {
 }
 ```
 
+### Removed: old `app.render()` signature (Adapter API)
+
+<SourcePR number="14462" title="feat: clean deprecated APIs"/>
+
+In Astro 4.0, the `app.render()` signature that allowed passing `routeData` and `locals` as optional arguments was deprecated in favor of a single optional `renderOptions` argument.
+
+Astro 6.0 removes this signature entirely. Attempting to pass these separate arguments will now cause an error in your project.
+
+#### What should I do?
+
+Review your `app.render` calls and pass `routeData` and `locals` as properties of an object instead of as multiple independent arguments:
+
+```ts title="my-adapter/entrypoint.ts" del={1} ins={2}
+app.render(request, routeData, locals)
+app.render(request, { routeData, locals })
+```
+
+<ReadMore>Learn more about the [Adapter API](/en/reference/adapter-reference/).</ReadMore>
+
+### Removed: `handleForms` prop for the `<ClientRouter />` component
+
+<SourcePR number="14462" title="feat: clean deprecated APIs"/>
+
+In Astro 4.0, the `handleForms` prop of the `<ClientRouter />` component was deprecated, as it was no longer necessary to opt in to handling `submit` events for `form` elements. This functionality has been built-in by default and the property, if still included in your project, silently had no impact on form submission.
+
+Astro 6.0 removes this prop entirely and it now must be removed to avoid errors in your project.
+
+#### What should I do?
+
+Remove the `handleForms` property from your `<ClientRouter />` component if it exists. It has provided no additional functionality, and so removing it should not change any behavior in your project:
+
+```astro title="src/pages/index.astro" del="handleForms"
+---
+import { ClientRouter } from "astro:transitions";
+---
+<html>
+  <head>
+    <ClientRouter handleForms />
+  </head>
+  <body>
+    <!-- stuff here -->
+  </body>
+</html>
+```
+
+<ReadMore>Learn more about [transitions with forms](/en/guides/view-transitions/#transitions-with-forms).</ReadMore>
+
+### Removed: `prefetch()` `with` option
+
+<SourcePR number="14462" title="feat: clean deprecated APIs"/>
+
+In Astro 4.8.4, the `with` option of the programmatic `prefetch()` function was deprecated in favor of a more sensible default behavior that no longer required specifying the priority of prefetching for each page.
+
+Astro 6.0 removes this option entirely and it is no longer possible to configure the priority of prefetching by passing the `with` option. Attempting to do so will now cause errors.
+
+By default, Astro's prefetching now uses an automatic approach that will always try to use `<link rel="prefetch>` if supported, or will fall back to `fetch()`.
+
+#### What should I do?
+
+Review your `prefetch()` calls and remove the `with` option if it still exists:
+
+```ts
+prefetch('/about', { with: 'fetch' });
+prefetch('/about');
+```
+
+<ReadMore>Learn more about [prefetching](/en/guides/prefetch/).</ReadMore>
+
 ## Changed Defaults
 
 Some default behavior has changed in Astro v5.0 and your project code may need updating to account for these changes.