issue 43828

Author: Cam Soper

docs/core/compatibility/10.0.md

@@ -24,6 +24,12 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | [C# 14 overload resolution with span parameters](core-libraries/10.0/csharp-overload-resolution.md)                        | Behavioral change   | Preview 1          |
 | [LDAP DirectoryControl parsing is now more stringent](core-libraries/10.0/ldap-directorycontrol-parsing.md)                | Behavioral change   | Preview 1          |
 
+## Globalization
+
+| Title                                                                                                 | Type of change    | Introduced version |
+|-------------------------------------------------------------------------------------------------------|-------------------|--------------------|
+| [Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE](globalization/10.0/version-override.md) | Behavioral change | Preview 1          |
+
 ## Windows Forms
 
 | Title                                                                                              | Type of change      | Introduced version |

docs/core/compatibility/globalization/10.0/version-override.md

@@ -0,0 +1,32 @@
+---
+title: "Breaking change: Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE"
+description: Learn about the .NET 10 breaking change in core .NET libraries where the environment variable CLR_ICU_VERSION_OVERRIDE was renamed to DOTNET_ICU_VERSION_OVERRIDE.
+ms.date: 01/30/2025
+---
+# Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE
+
+.NET has previously supported a configuration switch environment variable called `CLR_ICU_VERSION_OVERRIDE`, which allows users to specify the preferred ICU library version for apps running on Linux. In .NET 10, this environment variable has been renamed to `DOTNET_ICU_VERSION_OVERRIDE` to align with the naming convention of other configuration switch environment variables in .NET.
+
+## Previous behavior
+
+The `CLR_ICU_VERSION_OVERRIDE` environment variable is used to specify the preferred ICU version to be loaded in the application.
+
+## New behavior
+
+The `DOTNET_ICU_VERSION_OVERRIDE` environment variable is used to specify the preferred ICU version to be loaded in the application.
+
+## Version introduced
+
+.NET 10 Preview 1
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+This change ensures the environment variable is consistent with the naming convention used for all .NET environment variables.
+
+## Recommended action
+
+Users running .NET 10 apps who previously used the `CLR_ICU_VERSION_OVERRIDE` environment variable will now need to use `DOTNET_ICU_VERSION_OVERRIDE` instead.

docs/core/compatibility/toc.yml

@@ -18,6 +18,10 @@ items:
                 href: core-libraries/10.0/csharp-overload-resolution.md
               - name: LDAP DirectoryControl parsing is now more stringent
                 href: core-libraries/10.0/ldap-directorycontrol-parsing.md
+          - name: Globalization
+            items:
+              - name: Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE
+                href: globalization/10.0/version-override.md
           - name: Windows Forms
             items:
               - name: TreeView checkbox image truncation
@@ -1690,6 +1694,10 @@ items:
                 href: extensions/6.0/service-provider-disposed.md
       - name: Globalization
         items:
+          - name: .NET 10
+            items:
+              - name: Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE
+                href: globalization/10.0/version-override.md
           - name: .NET 8
             items:
               - name: Date and time converters honor culture argument