diff --git a/src/content/spec/foundations/open-graph.md b/src/content/spec/foundations/open-graph.md
index 500f0a68..fce4f789 100644
--- a/src/content/spec/foundations/open-graph.md
+++ b/src/content/spec/foundations/open-graph.md
@@ -7,7 +7,7 @@ status: recommended
 order: 100
 appliesTo: [all]
 relatedSlugs: [title, meta-description, canonical-url, favicons, localised-metadata]
-updated: "2026-06-08T00:00:00.000Z"
+updated: "2026-06-09T00:00:00.000Z"
 sources:
   - title: "The Open Graph protocol"
     url: "https://ogp.me/"
@@ -15,9 +15,6 @@ sources:
   - title: "A Guide to Sharing for Webmasters"
     url: "https://developers.facebook.com/docs/sharing/webmasters/"
     publisher: "Meta"
-  - title: "MDN — The Open Graph protocol"
-    url: "https://developer.mozilla.org/en-US/docs/Web/OpenGraph"
-    publisher: "MDN"
   - title: "X — About Cards"
     url: "https://developer.x.com/en/docs/x-for-websites/cards/overview/abouts-cards"
     publisher: "X"
diff --git a/src/content/spec/i18n/hreflang.md b/src/content/spec/i18n/hreflang.md
index a097fafc..5065b247 100644
--- a/src/content/spec/i18n/hreflang.md
+++ b/src/content/spec/i18n/hreflang.md
@@ -7,10 +7,10 @@ status: recommended
 order: 10
 appliesTo: [all]
 relatedSlugs: [lang-attribute, locale-content, rtl-support, international-url-structure, sitemap-hreflang, localised-metadata, language-switcher, avoid-auto-geo-redirects]
-updated: "2026-05-31T00:00:00.000Z"
+updated: "2026-06-09T00:00:00.000Z"
 sources:
   - title: "Google Search Central — Localized versions of your pages"
-    url: "https://developers.google.com/search/docs/specialized/international/localized-versions"
+    url: "https://developers.google.com/search/docs/specialty/international/localized-versions"
     publisher: "Google Search Central"
   - title: "BCP 47 — Tags for Identifying Languages"
     url: "https://www.rfc-editor.org/info/bcp47"
diff --git a/src/content/spec/privacy/global-privacy-control.md b/src/content/spec/privacy/global-privacy-control.md
index 8dbf069b..47b7d386 100644
--- a/src/content/spec/privacy/global-privacy-control.md
+++ b/src/content/spec/privacy/global-privacy-control.md
@@ -7,10 +7,10 @@ status: recommended
 order: 30
 appliesTo: [all]
 relatedSlugs: [cookie-consent, privacy-policy, analytics-privacy]
-updated: "2026-05-29T09:13:20.000Z"
+updated: "2026-06-09T00:00:00.000Z"
 sources:
   - title: "Global Privacy Control specification"
-    url: "https://globalprivacycontrol.github.io/gpc-spec/"
+    url: "https://w3c.github.io/gpc/"
     publisher: "W3C Community Group"
   - title: "California Attorney General — Frequently Asked Questions: CCPA"
     url: "https://oag.ca.gov/privacy/ccpa"
diff --git a/src/content/spec/security/content-security-policy.md b/src/content/spec/security/content-security-policy.md
index 1fd8b535..e91eee42 100644
--- a/src/content/spec/security/content-security-policy.md
+++ b/src/content/spec/security/content-security-policy.md
@@ -6,7 +6,7 @@ summary: "A CSP tells browsers which sources of script, style, image, and frame
 status: recommended
 order: 30
 appliesTo: [all]
-relatedSlugs: [https-tls, frame-ancestors, subresource-integrity, permissions-policy, mixed-content]
+relatedSlugs: [https-tls, frame-ancestors, subresource-integrity, permissions-policy, mixed-content, cross-origin-isolation]
 updated: "2026-06-08T20:15:00.000Z"
 sources:
   - title: "Content Security Policy Level 3"
diff --git a/src/content/spec/security/cross-origin-isolation.md b/src/content/spec/security/cross-origin-isolation.md
new file mode 100644
index 00000000..11ff461a
--- /dev/null
+++ b/src/content/spec/security/cross-origin-isolation.md
@@ -0,0 +1,75 @@
+---
+title: "Cross-origin isolation (COOP / COEP / CORP)"
+slug: cross-origin-isolation
+category: security
+summary: "Three response headers — Cross-Origin-Opener-Policy, Cross-Origin-Embedder-Policy, and Cross-Origin-Resource-Policy — that sever risky cross-window and cross-origin links and defend against side-channel leaks."
+status: recommended
+order: 65
+appliesTo: [all]
+relatedSlugs: [frame-ancestors, content-security-policy, permissions-policy, referrer-policy]
+updated: "2026-06-11T00:00:00.000Z"
+sources:
+  - title: "HTML Standard — Cross-Origin-Opener-Policy"
+    url: "https://html.spec.whatwg.org/multipage/browsers.html#the-coop-headers"
+    publisher: "WHATWG"
+  - title: "Fetch Standard — Cross-Origin-Resource-Policy header"
+    url: "https://fetch.spec.whatwg.org/#cross-origin-resource-policy-header"
+    publisher: "WHATWG"
+  - title: "MDN — Cross-Origin-Opener-Policy"
+    url: "https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cross-Origin-Opener-Policy"
+    publisher: "MDN"
+  - title: "MDN — Cross-Origin-Resource-Policy"
+    url: "https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cross-Origin-Resource-Policy"
+    publisher: "MDN"
+---
+
+## What it is
+
+Three response headers that control how your documents and resources relate to other origins:
+
+- **`Cross-Origin-Opener-Policy` (COOP)** severs the `window.opener` link between your page and the page that opened it, placing your document in its own browsing context group. Values: `unsafe-none` (default), `same-origin-allow-popups`, `same-origin`, and the newer `noopener-allow-popups`.
+- **`Cross-Origin-Resource-Policy` (CORP)** tells the browser which origins may embed a resource — your images, scripts, fonts — as a `no-cors` subresource. Values: `same-origin`, `same-site`, `cross-origin`.
+- **`Cross-Origin-Embedder-Policy` (COEP)** requires every subresource your document loads to opt in via CORP or CORS. Values: `unsafe-none`, `require-corp`, `credentialless`.
+
+```http
+Cross-Origin-Opener-Policy: same-origin
+Cross-Origin-Resource-Policy: same-site
+```
+
+## Why it matters
+
+When a user follows a link off your site — or arrives on your site from someone else's link — the two pages can keep a live connection through the `window.opener` handle. A malicious page can abuse that connection: the moment the user's attention is elsewhere, it can silently swap the tab it opened to a pixel-perfect fake of your login screen (a "tabnabbing" attack), or quietly probe which sites the user is signed in to. The user notices nothing and types their password into the impostor. COOP cuts that connection, so a page on another origin can no longer reach back into yours.
+
+CORP guards your resources from the opposite direction, and the threat it answers needs a word of background. **Spectre** is a family of processor flaws, disclosed in 2018, that let code read areas of memory it should never be allowed to see — including data belonging to _other_ websites that happen to be running in the same browser process. A page could exploit it to read your signed-in user's private data — their email, their account balance — without ever making a normal request for it. The browser's defence is to keep each origin's data out of processes that have no business touching it; CORP is how a resource declares "only my own site may embed me," so it is never pulled into an attacker's process in the first place. ([web.dev — Why you need cross-origin isolation](https://web.dev/articles/why-coop-coep) explains the attack and the fix in depth.)
+
+The practical payoff is high and the cost is near zero: setting COOP and CORP closes off a whole category of invisible cross-site snooping — no consent prompt, no broken functionality, no measurable performance hit. The user is simply safer and never has to know the headers exist.
+
+Setting COOP `same-origin` together with COEP additionally unlocks **cross-origin isolation** (`crossOriginIsolated === true`) — the browser's confirmation that your page is fully walled off from other origins. Only once that holds will the browser hand your page the powerful, isolation-gated APIs such as `SharedArrayBuffer` and unthrottled high-resolution timers.
+
+This site ships `Cross-Origin-Opener-Policy: same-origin` and `Cross-Origin-Resource-Policy: same-site` on every response — see [`public/_headers`](https://github.com/jdevalk/specification.website/blob/main/public/_headers).
+
+## How to implement
+
+Send COOP and CORP on every HTML response as a baseline:
+
+```http
+Cross-Origin-Opener-Policy: same-origin
+Cross-Origin-Resource-Policy: same-site
+```
+
+If your site relies on OAuth or payment pop-ups, relax COOP to `same-origin-allow-popups` so the pop-up flow keeps working while isolated pages stay protected.
+
+Only add `Cross-Origin-Embedder-Policy: require-corp` if you actually need `SharedArrayBuffer` or other isolation-gated APIs — it forces every cross-origin subresource to opt in, which often breaks third-party embeds until each one sends CORP or CORS. Treat full isolation as opt-in, not a default.
+
+## Common mistakes
+
+- **Reaching for `require-corp` without needing isolation.** It breaks embeds for no benefit unless an isolation-gated API is in use.
+- **`same-origin` COOP on pages that depend on pop-up callbacks.** Use `same-origin-allow-popups` there.
+- **Serving CORP `same-origin` on assets meant to be hot-linked** (a public CDN, embeddable widget). Use `cross-origin` for genuinely public resources.
+- **Setting the headers on HTML but not on the resources** other sites legitimately embed.
+
+## Verification
+
+- `curl -sI https://example.com | grep -iE 'cross-origin-(opener|resource|embedder)-policy'`.
+- In DevTools, read `self.crossOriginIsolated` — `true` confirms COOP `same-origin` + COEP `require-corp` are both in force.
+- Check the **Application → Frames** panel for COOP/COEP status reported per document.
diff --git a/src/content/spec/security/frame-ancestors.md b/src/content/spec/security/frame-ancestors.md
index 638c2d96..b6e87ef6 100644
--- a/src/content/spec/security/frame-ancestors.md
+++ b/src/content/spec/security/frame-ancestors.md
@@ -6,7 +6,7 @@ summary: "Tell browsers who is allowed to embed your pages in an iframe. Use CSP
 status: required
 order: 60
 appliesTo: [all]
-relatedSlugs: [content-security-policy, x-content-type-options, permissions-policy]
+relatedSlugs: [content-security-policy, x-content-type-options, permissions-policy, cross-origin-isolation]
 updated: "2026-05-29T09:13:20.000Z"
 sources:
   - title: "OWASP — Clickjacking Defense Cheat Sheet"
diff --git a/src/content/spec/security/permissions-policy.md b/src/content/spec/security/permissions-policy.md
index 12620054..b3f516f3 100644
--- a/src/content/spec/security/permissions-policy.md
+++ b/src/content/spec/security/permissions-policy.md
@@ -6,7 +6,7 @@ summary: "Permissions-Policy lets you turn off powerful browser features — cam
 status: recommended
 order: 80
 appliesTo: [all]
-relatedSlugs: [content-security-policy, frame-ancestors, referrer-policy]
+relatedSlugs: [content-security-policy, frame-ancestors, referrer-policy, cross-origin-isolation]
 updated: "2026-05-29T09:13:20.000Z"
 sources:
   - title: "Permissions Policy (W3C Working Draft)"