Add deprecation notice for Copilot extensions (#57626)

Co-authored-by: Ben Ahmady <32935794+subatoi@users.noreply.github.com>

Author: D1M1TR10S

content/copilot/concepts/context/copilot-extensions.md

@@ -16,6 +16,14 @@ redirect_from:
 contentType: concepts
 ---
 
+<!-- expires 2025-11-19 -->
+
+<!-- When this expires, check with the stakeholder for release #6165 if the knowledge bases content can be deleted -->
+
+{% data reusables.copilot.copilot-extensions.extensions-retirement %}
+
+<!-- end expires 2025-11-19 -->
+
 ## About {% data variables.copilot.copilot_extensions_short %}
 
 {% data reusables.copilot.copilot-extensions.about-copilot-extensions %}

content/copilot/concepts/extensions/build-extensions.md

@@ -16,6 +16,14 @@ redirect_from:
 contentType: concepts
 ---
 
+<!-- expires 2025-11-19 -->
+
+<!-- When this expires, check with the stakeholder for release #6165 if the knowledge bases content can be deleted -->
+
+{% data reusables.copilot.copilot-extensions.extensions-retirement %}
+
+<!-- end expires 2025-11-19 -->
+
 ## About building {% data variables.copilot.copilot_extensions_short %}
 
 {% data reusables.copilot.copilot-extensions.about-copilot-extensions %}

content/copilot/how-tos/provide-context/install-copilot-extensions/use-copilot-extensions.md

@@ -17,6 +17,14 @@ redirect_from:
 contentType: how-tos
 ---
 
+<!-- expires 2025-11-19 -->
+
+<!-- When this expires, check with the stakeholder for release #6165 if the knowledge bases content can be deleted -->
+
+{% data reusables.copilot.copilot-extensions.extensions-retirement %}
+
+<!-- end expires 2025-11-19 -->
+
 ## About {% data variables.copilot.copilot_extensions %}
 
 {% data reusables.copilot.copilot-extensions.copilot-extensions-intro %}

content/copilot/how-tos/use-copilot-extensions/set-up-copilot-extensions.md

@@ -14,6 +14,14 @@ redirect_from:
 contentType: how-tos
 ---
 
+<!-- expires 2025-11-19 -->
+
+<!-- When this expires, check with the stakeholder for release #6165 if the knowledge bases content can be deleted -->
+
+{% data reusables.copilot.copilot-extensions.extensions-retirement %}
+
+<!-- end expires 2025-11-19 -->
+
 This article is designed to help you build an entirely new {% data variables.copilot.copilot_extension %}. To instead learn how to quickly build and test a demo {% data variables.copilot.copilot_extension_short %} created by {% data variables.product.github %}, see [AUTOTITLE](/copilot/building-copilot-extensions/quickstart-for-github-copilot-extensions).
 
 {% data reusables.copilot.copilot-extensions.differences-between-agents-and-skillsets-1 %}

data/reusables/copilot/copilot-extensions/extensions-retirement.md

@@ -0,0 +1,10 @@
+> [!IMPORTANT]
+> {% data variables.copilot.copilot_extensions_short %} built as {% data variables.product.prodname_github_apps %} will be closing down on November 10, 2025. {% data variables.product.prodname_vscode_shortname %} {% data variables.copilot.copilot_extensions_short %} are not affected and will remain supported.
+>
+> Key dates:
+> * September 23, 2025: New creation of {% data variables.copilot.copilot_extensions_short %} will be blocked
+> * November 10, 2025: All existing {% data variables.copilot.copilot_extensions_short %} will be disabled
+>
+> Consider building MCP servers to replace extension functionality where applicable. Hybrid apps (with other {% data variables.product.prodname_github_app %} functionality) must disable the {% data variables.copilot.copilot_extension_short %} configuration in app settings to remain listed in the {% data variables.product.prodname_marketplace %} after November 10, 2025.
+>
+> For more information, see the [changelog announcement](https://github.blog/changelog/2025-09-23-deprecate-github-copilot-extensions-github-apps/).