diff --git a/.changeset/shy-cats-grin.md b/.changeset/shy-cats-grin.md
new file mode 100644
index 000000000000..95667b845602
--- /dev/null
+++ b/.changeset/shy-cats-grin.md
@@ -0,0 +1,5 @@
+---
+'astro': major
+---
+
+Removes the `setManifestData` method from `App` and `NodeApp` (Adapter API) - ([v6 upgrade guidance](https://deploy-preview-12322--astro-docs-2.netlify.app/en/guides/upgrade-to/v6/#removed-appsetmanifestdata-adapter-api))
\ No newline at end of file
diff --git a/packages/astro/src/core/app/index.ts b/packages/astro/src/core/app/index.ts
index 0734a09673ab..4795361f2595 100644
--- a/packages/astro/src/core/app/index.ts
+++ b/packages/astro/src/core/app/index.ts
@@ -297,10 +297,6 @@ export class App {
 		});
 	}
 
-	set setManifestData(newManifestData: RoutesList) {
-		this.#manifestData = newManifestData;
-	}
-
 	removeBase(pathname: string) {
 		if (pathname.startsWith(this.#manifest.base)) {
 			return pathname.slice(this.#baseWithoutTrailingSlash.length + 1);