diff --git a/.changeset/23806-metadata-core-vitest-peer.md b/.changeset/23806-metadata-core-vitest-peer.md
new file mode 100644
index 0000000000..f654b9de11
--- /dev/null
+++ b/.changeset/23806-metadata-core-vitest-peer.md
@@ -0,0 +1,22 @@
+---
+'@objectstack/metadata-core': patch
+---
+
+fix(metadata-core): the package installs on npm 10 again, and into projects that use vitest 5, because it no longer declares an optional `vitest` peer
+
+Clause-②: no
+
+On npm 10, the npm that Node 22 bundles, `npm install @objectstack/metadata-core` exited 1 with `Cannot read properties of null (reading 'edgesOut')`. So did installing a package that depends on it, such as `@objectstack/objectql`. The cause was this package's optional peer `vitest: ^4.0.0`. It led npm 10 to vitest 4.1.12, whose own peer declarations contradict each other, and npm 10's resolver crashes on that. The same peer also made npm refuse (`ERESOLVE`) to install the package into a project that already uses vitest 5.
+
+The package's main entry never imports `vitest`. Only the test-only `@objectstack/metadata-core/testing` entry does, so the peer is removed. Nothing the package exports changes.
+
+If you import `@objectstack/metadata-core/testing`, list `vitest` in your own `devDependencies`, as that entry's documentation already says. This package runs that suite on vitest 4. In a pnpm workspace with hoisting turned off (`hoist=false`), that entry can no longer find `vitest` from inside a workspace package. Declare the peer back in your `pnpm-workspace.yaml`:
+
+```yaml
+packageExtensions:
+  '@objectstack/metadata-core':
+    peerDependencies:
+      vitest: '*'
+```
+
+`@objectstack/plugin-auth` still fails the same way on npm 10, because its `better-auth` dependency declares its own optional `vitest` peer. Install it with npm 11, or add `"overrides": { "vitest": "~4.0.0" }` to your project's `package.json`.
diff --git a/packages/metadata-core/package.json b/packages/metadata-core/package.json
index 20303fafd8..081ebded17 100644
--- a/packages/metadata-core/package.json
+++ b/packages/metadata-core/package.json
@@ -45,14 +45,6 @@
     "@objectstack/spec": "workspace:*",
     "zod": "^4.6.5"
   },
-  "peerDependencies": {
-    "vitest": "^4.0.0"
-  },
-  "peerDependenciesMeta": {
-    "vitest": {
-      "optional": true
-    }
-  },
   "devDependencies": {
     "@types/node": "^26.6.3",
     "fast-check": "^4.10.2",