d .Merge branch 'main' of https://github.com/MicrosoftDocs/azure-docs-pr

Author: MekaylaMoore

articles/expressroute/gateway-migration.md

@@ -67,6 +67,28 @@ The guided gateway migration experience has the following limitations:
 
 For detailed troubleshooting errors and best practices, see [Troubleshooting Gateway Migration](gateway-migration-error-messaging.md).
 
+## Gateway migration experience
+
+The gateway migration experience allows you to deploy a second virtual network gateway in the same GatewaySubnet. Azure migrates your configurations from the old gateway to the new one. Both gateways run simultaneously during migration, minimizing disruption – though brief connectivity interruptions may still occur.
+
+After migration, the old gateway and its connections are deleted, and the new gateway is tagged with **CreatedBy: GatewaySKUMigration** to identify it as a migrated resource and shouldn’t be deleted.
+
+### Steps to migrate to a new gateway
+
+1. **Validate**: Check that all resources are in a succeeded state. If any prerequisites aren't met, validation fails and migration can't proceed.
+2. **Prepare**: Azure creates a new virtual network gateway, public IP, and connections. This step can take up to 45 minutes. You can specify a name for the new gateway, or Azure will add **_migrate** to the original name by default. During preparation, the existing gateway is locked to prevent changes. If you need to stop the migration, you can **abort** at this stage, which deletes the new gateway and connections.
+    - **Note**: The new gateway is created in the same region as the existing one. To change regions, you must delete the current gateway and create a new one in the desired region.
+3. **Migrate**: Switch traffic from the old gateway to the new one. This step can take up to 15 minutes and may cause brief connectivity interruptions.
+4. **Commit**: Complete the migration by deleting the old gateway and its connections. If necessary, you can abort and revert to the old gateway before committing.
+
+
+> [!IMPORTANT]
+> After migration, validate your connectivity to ensure everything is functioning as expected. You can revert to the old gateway by selecting **Abort** after the prepare step, which will delete the new gateway and connections.
+
+| Migration source (Non-Az-enabled gateway SKU) | Migration target (Az-enabled gateway SKU) |
+|--|--|
+| Basic IP | Standard IP |
+
 ## FAQ
 
 ### How do I add a second prefix to the GatewaySubnet?