diff --git a/build/hygiene.ts b/build/hygiene.ts
index 86cf3b17346d9..e7c44a569a353 100644
--- a/build/hygiene.ts
+++ b/build/hygiene.ts
@@ -92,9 +92,14 @@ export function hygiene(some: NodeJS.ReadWriteStream | string[] | undefined, run
 	const productJson = es.through(function (file: VinylFile) {
 		const product = JSON.parse(file.contents!.toString('utf8'));
 
+		// Block Microsoft Marketplace (and other non-OSS galleries) in product.json.
+		// Open VSX is allowed — see https://github.com/eclipse-openvsx/openvsx/wiki/Using-Open-VSX-in-VS-Code
 		if (product.extensionsGallery) {
-			console.error(`product.json: Contains 'extensionsGallery'`);
-			errorCount++;
+			const serviceUrl = String(product.extensionsGallery.serviceUrl ?? '');
+			if (!/^https:\/\/open-vsx\.org(\/|$)/.test(serviceUrl)) {
+				console.error(`product.json: Contains 'extensionsGallery' (only https://open-vsx.org is allowed)`);
+				errorCount++;
+			}
 		}
 
 		this.emit('data', file);
diff --git a/product.json b/product.json
index f3f91db9fabb2..9cad8d336299e 100644
--- a/product.json
+++ b/product.json
@@ -37,6 +37,15 @@
 	"urlProtocol": "code-oss",
 	"agentsTelemetryAppName": "agents",
 	"webviewContentExternalBaseUrlTemplate": "https://{{uuid}}.vscode-cdn.net/insider/ef65ac1ba57f57f2a3961bfe94aa20481caca4c6/out/vs/workbench/contrib/webview/browser/pre/",
+	"extensionsGallery": {
+		"serviceUrl": "https://open-vsx.org/vscode/gallery",
+		"itemUrl": "https://open-vsx.org/vscode/item",
+		"resourceUrlTemplate": "https://open-vsx.org/vscode/unpkg/{publisher}/{name}/{version}/{path}",
+		"extensionUrlTemplate": "https://open-vsx.org/vscode/gallery/{publisher}/{name}/latest"
+	},
+	"linkProtectionTrustedDomains": [
+		"https://open-vsx.org"
+	],
 	"builtInExtensions": [
 		{
 			"name": "ms-vscode.js-debug-companion",
diff --git a/screenshots/code-oss-after-dismiss.png b/screenshots/code-oss-after-dismiss.png
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index 0000000000000..a2af74504706b
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diff --git a/screenshots/code-oss-final.png b/screenshots/code-oss-final.png
new file mode 100644
index 0000000000000..72b9df7c9d5f2
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diff --git a/screenshots/code-oss-ui.png b/screenshots/code-oss-ui.png
new file mode 100644
index 0000000000000..01a1f63c5e026
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diff --git a/screenshots/openvsx-search.png b/screenshots/openvsx-search.png
new file mode 100644
index 0000000000000..493728ec4d97b
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diff --git a/screenshots/openvsx-search2.png b/screenshots/openvsx-search2.png
new file mode 100644
index 0000000000000..e66a5b73103a4
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diff --git a/screenshots/recommended-zero.png b/screenshots/recommended-zero.png
new file mode 100644
index 0000000000000..2568224f7ba56
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